U.S. patent number 6,281,289 [Application Number 09/456,595] was granted by the patent office on 2001-08-28 for polypropylene/ethylene polymer fiber having improved bond performance and composition for making the same.
This patent grant is currently assigned to The Dow Chemical Company. Invention is credited to Edward N. Knickerbocker, Rexford A. Maugans, Kenneth B. Stewart.
United States Patent |
6,281,289 |
Maugans , et al. |
August 28, 2001 |
Polypropylene/ethylene polymer fiber having improved bond
performance and composition for making the same
Abstract
The subject invention is directed to fibers and polymer blend
compositions having improved bonding performance. In particular,
the subject invention pertains to a multiconstituent fiber
comprising a blend of a polypropylene polymer and a high molecular
weight (i.e. low melt index or melt flow) ethylene polymer. The
subject invention further pertains to the use of the fiber and
polymer blend composition which has improved bonding performance in
various end-use applications, especially woven and nonwoven fabrics
such as, for example, disposable incontinence garments and diapers.
The fibers have good spinnability and provide fabrics having
improved bond strength and elongation.
Inventors: |
Maugans; Rexford A. (Lake
Jackson, TX), Knickerbocker; Edward N. (Lake Jackson,
TX), Stewart; Kenneth B. (Lake Jackson, TX) |
Assignee: |
The Dow Chemical Company
(Midland, MI)
|
Family
ID: |
22338582 |
Appl.
No.: |
09/456,595 |
Filed: |
December 8, 1999 |
Current U.S.
Class: |
525/191;
525/240 |
Current CPC
Class: |
C08L
23/10 (20130101); D01F 6/46 (20130101); C08L
23/10 (20130101); C08L 23/0815 (20130101); C08L
2314/06 (20130101); Y10T 428/298 (20150115); Y10T
428/2929 (20150115); Y10T 428/2933 (20150115); C08L
2666/04 (20130101) |
Current International
Class: |
C08L
23/00 (20060101); C08L 23/10 (20060101); D01F
6/46 (20060101); C08L 23/08 (20060101); C08F
008/00 (); C08L 023/00 (); C08L 023/04 () |
Field of
Search: |
;525/191,240 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4584347 |
April 1986 |
Harpell et al. |
5486419 |
January 1996 |
Clementini et al. |
6080818 |
June 2000 |
Thakker et al. |
|
Primary Examiner: Nutter; Nathan M.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of US provisional
application No. 60/111,443, filed Dec. 8, 1998, the disclosure of
which is incorporated herein by reference, in its entirety.
Claims
We claim:
1. A fiber having a diameter in a range of from 0.1 to 50 denier
and comprising:
(A) from about 0.1 percent to about 30 weight percent (by weight of
the fiber) of at least one ethylene polymer having:
i. an I.sub.2 melt index less than or equal to 10 grams/10 minutes,
and
ii. a density of from about 0.85 to about 0.97
grams/centimeters.sup.3, and
(B) a polypropylene polymer,
wherein the ethylene polymer is an ethylene homopolymer or
ethylene/.alpha.-olefin interpolymer having a density greater than
or equal to 0.94 g/cm.sup.3, the I.sub.2 melt index of the ethylene
polymer is less than 5 g/10 minutes, and wherein the fiber is
characterized as being thermal bondable at 340 pounds/linear inch
(pli) and a bond roll surface temperature in the range of 127 to
137.degree. C.
2. The fiber of claim 1, wherein the fiber comprises from about 0.5
to about 22 weight percent of the ethylene polymer.
3. The fiber of claim 1, wherein the ethylene polymer is an
interpolymer of ethylene and at least one C.sub.3 -C.sub.20
.alpha.-olefin.
4. The fiber of claim 1, wherein the ethylene polymer is a
substantially linear ethylene/.alpha.-olefin interpolymer
characterized as having:
a. a melt flow ratio (I.sub.10 /I.sub.2).gtoreq.5.63,
b. a molecular weight distribution, M.sub.w /M.sub.n, defined by
the inequality:
and
c. a critical shear rate at the onset of surface melt fracture
which is at least 50 percent greater than the critical shear rate
at the onset of surface melt fracture of a linear
ethylene/.alpha.-olefin interpolymer having the about same I.sub.2
and M.sub.w /M.sub.n.
5. The fiber of claim 1, wherein the polypropylene polymer is a
reactor grade polypropylene and has a MFR at 230.degree. C./2.16 kg
greater than or equal 20 g/10 minutes.
6. The fiber of claim 1, wherein the polypropylene polymer is a
visbroken polypropylene and has a melt flow rate at 230.degree.
C./2.16 kg of greater than or equal 20 g/10 minutes.
7. The fiber of claim 1, wherein the polypropylene polymer has a
coupled melt flow rate at 230.degree. C./2.16 kg of greater than or
equal 20 g/10 minutes.
8. The fiber of claim 1, wherein the polypropylene polymer is
manufactured using a single-site, metallocene or constrained
geometry catalyst system.
9. The fiber of claim 1, wherein the polypropylene polymer is
characterized as having at least 96 percent weight
isotacticity.
10. The fiber of claim 1, wherein the fibers are prepared by a melt
spinning process such that the fibers are melt blown fibers,
spunbonded fibers, carded staple fibers or flash spun fibers.
Description
FIELD OF THE INVENTION
This invention relates to polymer compositions having improved
bonding performance. In particular, the subject invention pertains
to a polymer composition comprising a blend of a polypropylene
polymer and a high molecular weight (i.e. low melt index or melt
flow) ethylene polymer. The subject invention further pertains to
the use of the polymer blend composition which has improved bonding
performance in various end-use applications, especially fibers,
nonwoven fabrics and other articles fabricated from fibers (e.g.,
disposable incontinence garments and diapers). The fibers have good
spinnability and provide a fabric having good bond strength and
good elongation.
BACKGROUND
Fiber is typically classified according to its diameter.
Monofilament fiber is generally defined as having an individual
fiber diameter greater than 15 denier, usually greater than 30
denier per filament. Fine denier fiber generally refers to a fiber
having a diameter less than 15 denier per filament. Microdenier
fiber is generally defined as fiber having less than 100 microns
diameter. The fiber can also be classified by the process by which
it is made, such as monofilament, continuous wound fine filament,
staple or short cut fiber, spun bond, and melt blown fiber.
A variety of fibers and fabrics have been made from thermoplastics,
such as polypropylene, highly branched low density polyethylene
(LDPE) made typically in a high pressure polymerization process,
linear heterogeneously branched polyethylene (e.g., linear low
density polyethylene made using Ziegler catalysis), blends of
polypropylene and linear heterogeneously branched polyethylene,
blends of linear heterogeneously branched polyethylene, and
ethylene/vinyl alcohol copolymers.
Of the various polymers known to be extrudable into fiber, highly
branched LDPE has not been successfully melt spun into fine denier
fiber. Linear heterogeneously branched polyethylene has been made
into monofilament, as described in U.S. Pat. No. 4,076,698
(Anderson et al.), the disclosure of which is incorporated herein
by reference. Linear heterogeneously branched polyethylene has also
been successfully made into fine denier fiber, as disclosed in U.S.
Pat. No. 4,644,045 (Fowells), U.S. Pat. No. 4,830,907 (Sawyer et
al.), U.S. Pat. No. 4,909,975 (Sawyer et al.) and. in U.S. Pat. No.
4,578,414 (Sawyer et al.), the disclosures of which are
incorporated herein by reference. Blends of such heterogeneously
branched polyethylene have also been successfully made into fine
denier fiber and fabrics, as disclosed in U.S. Pat. No. 4,842,922
(Krupp et al.), U.S. Pat. No. 4,990,204 (Krupp et al.) and U.S.
Pat. No. 5,112,686 (Krupp et al.), the disclosures of which are all
incorporated herein by reference. U.S. Pat. No. 5,068,141 (Kubo et
al.) also discloses making nonwoven fabrics from continuous heat
bonded filaments of certain heterogeneously branched LLDPE having
specified heats of fusion. While the use of blends of
heterogeneously branched polymers produces improved fabric, the
polymers are more difficult to spin without fiber breaks and/or
dripping at the spinneret die.
U.S. Pat. Nos. 5,294,492 and 5,593,768 (Gessner), both incorporated
herein by reference, describe a multiconstituent fiber having
improved thermal bonding characteristics composed of a blend of at
least two different thermoplastic polymers which form a continuous
polymer phase and at least one noncontinuous polymer phase. In the
claims, Gessner recites that the at least one noncontinuous phase
occupies a substantial portion of the surface of the fiber made
from the blend. But while we believe the claims in U.S. Pat. Nos.
5,294,492 and 5,593,768 specify, for example, a core-sheath
configuration with respect to the polymer phases, the
photomicrograph (FIG. 1 therein) shows an island-sea type phase
configuration for the fiber cross-section. Further, we believe it
is the continuous polymer phase (not the noncontinuous phase) which
occupies a substantial portion of the surface of the fiber
exemplified (but not claimed) by Gessner. Also, all of the Examples
(and presumably FIG. 1 therein) consist of polypropylene polymer
blended with ASPUN.TM. fiber grade LLDPE resins having a 12 or 26
g/10 minute I.sub.2 melt index as supplied by The Dow Chemical
Company. The exemplar polypropylene polymer used by Gessner was
described a "controlled rheology" PP (i.e. a visbroken PP) having a
melt flow rate of 26 and at least 90 percent by weight
isotacticity.
U.S. Pat. No. 5,549,867 (Gessner et al.), incorporated herein by
reference, describes the addition of a low molecular weight (i.e.
high melt index or melt flow) polyolefin to a polyolefin with a
molecular weight (M.sub.z) of from 400,000 to 580,000 to improve
spinning. The Examples set forth in Gessner et al. are all directed
to blends of 10 to 30 weight percent of a lower molecular weight
metallocene polypropylene with from 70 to 90 weight percent of a
higher molecular weight polypropylene produced using a
Ziegler-Natta catalyst.
U.S. Pat. No. 4,839,228 (Jezic et al.), incorporated herein by
reference, describes biconstituent fibers having improved tenacity
and hand composed of a highly crystalline polypropylene polymer
with LDPE, HDPE or preferably LLDPE. The polyethylene resins are
described to have a moderately high molecular weight wherein their
I.sub.2 melt index is in the range of from about 12 to about 120
g/10 minutes.
Also, fibers made from blends of visbroken polypropylene polymer
and homopolymer high density polyethylene (HDPE) having an I.sub.2
melt index of equal to greater than 5 g/10 minutes are known. Such
blends are thought to function on the basis of the immiscibility of
the olefin polymers.
WO 95/32091 (Stahl et al.) discloses a reduction in bonding
temperatures by utilizing blends of fibers produced from
polypropylene resins having different melting points and produced
by different fiber manufacturing processes, e.g., meltblown and
spunbond fibers. Stahl et al. claims a fiber comprising a blend of
an isotactic propylene copolymer with a higher melting
thermoplastic polymer.
WO 96/23838, U.S. Pat. Nos. 5,539,056 and 5,516,848, the
disclosures of which are incorporated herein by reference, teach
blends of an amorphous poly-.alpha.-olefin of Mw>150,000
(produced via single site catalysis) and a crystalline
poly-.alpha.-olefin with Mw<300,000, (produced via single site
catalysis) in which the molecular weight of the amorphous
polypropylene is greater than the molecular weight of the
crystalline polypropylene. Preferred blends are described to
comprise about 10 to about 90 weight percent of amorphous
polypropylene. The described blends are said to exhibit unusual
elastomeric properties, namely an improved balance of mechanical
strength and rubber recovery properties.
U.S. Pat. No. 5,483,002 and EP 643100, the disclosures of both of
which are incorporated herein by reference, teach blends of a
semi-crystalline propylene homopolymer having a melting point of
125 to 165.degree. C. and a semi-crystalline propylene homopolymer
having a melting point below 130.degree. C. or a non-crystallizing
propylene homopolymer having a glass transition temperature which
is less than or equal to -10.degree. C. These blends are said to
have improved mechanical properties, notably impact strength.
Crystalline polypropylenes produced by single site catalysis have
been reported to be particularly suited for fiber production. Due
to narrow molecular weight distributions and low amorphous
contents, higher spinning rates and higher tenacities have been
reported. But, isotactic PP fibers, in general (and particularly
when produced using single site catalyst) exhibit poor bonding
performance.
U.S. Pat. No. 5,677,383 (Lai et al.), incorporated herein by
reference, discloses blends of (A) at least one homogeneously
branched ethylene polymer having a high slope of strain hardening
coefficient and (B) at least one ethylene polymer having a high
polymer density and some amount of a linear high density polymer
fraction. The Examples set forth by Lai et al. are directed to
substantially linear ethylene interpolymers blended with
heterogeneously branched ethylene polymers. Lai et al. describe the
use of their blends in a variety of end use applications, including
fibers. The disclosed compositions preferably comprise a
substantially linear ethylene polymer having a density of at least
0.89 grams/centimeters.sup.3. But Lai et al. disclosed fabrication
temperatures only above 165.degree. C. In contrast, to preserve
fiber integrity, fabrics are frequently bonded at temperatures less
than 165.degree. C. such that all of the crystalline material is
not melted before or during the fiber bonding step.
While various olefin polymer compositions have found success in a
number of fiber and fabric applications, the fibers made from such
compositions would benefit from an improvement in bond strength,
which would lead to stronger fabrics, and accordingly to increased
value to the nonwoven fabric and article manufacturers, as well as
to the ultimate consumer. But any benefit in bond strength must not
be at the cost of a detrimental reduction in spinnability and fiber
elongation nor a detrimental increase in the sticking of the fibers
or fabric to equipment during processing.
SUMMARY OF THE INVENTION
We have discovered that the inclusion of a high molecular weight
ethylene polymer into a polypropylene polymer provides a
multiconstituent fiber and calendered fabric having an improved
bond performance, while simultaneously maintaining excellent fiber
spinning and elongation performance. Accordingly, the subject
invention provides a fiber having a diameter in a range of from 0.1
to 50 denier and comprising:
(A) from about 0.5 percent to about 25 weight percent (by weight of
the fiber) of at least one ethylene polymer having:
i. an I.sub.2 melt index less than or equal to 10 grams/10 minutes,
preferably less than 5 g/10 minutes, more preferably less than or
equal to 3 g/10 minutes, most preferably less than or equal to 1.5
g/10 minutes, especially less than or equal to 0.75 g/10 minutes
and
ii. a density of from about 0.85 to about 0.97
grams/centimeters.sup.3, as measured in accordance with ASTM D792,
(or a corresponding percent crystallinity in range of about 12 to
about 81 percent by weight, as determined using differential
scanning calorimetry (DSC)), and
(B) a polypropylene polymer, preferably a polypropylene polymer
having a melt flow rate (MFR) in the range of about 1 to about 1000
grams/10 minutes, measured in accordance with ASTM D1238 at
230.degree. C./2.16 kg, more preferably in range of about 5 to
about 100 grams/10 minutes,
with the proviso that where the ethylene polymer is an
ethylene/.alpha.-olefin interpolymer having an I.sub.2 melt index
in the range of about 5 to about 10 g/10 minutes, the density of
the ethylene/.alpha.-olefin polymer is greater than 0.87
g/cm.sup.3, preferably greater than or equal to 0.90 g/cm.sup.3,
and more preferably greater than or equal to 0.94 g/cm.sup.3, as
measured in accordance with ASTM D792,
with the proviso that where the ethylene polymer is an ethylene
homopolymer or ethylene/.alpha.-olefin interpolymer having a
density greater than or equal to 0.94 g/cm.sup.3, as measured in
accordance with ASTM D792, the I.sub.2 melt index of the ethylene
polymer is less than 5 g/10 minutes, preferably less than or equal
to 3 g/10 minutes, more preferably less than or equal to 1.5 g/10
minutes, most preferably less than or equal to 0.75 g/10 minutes,
and wherein the fiber is thermal bondable at 340 pounds/linear inch
and a bond roll surface temperature in the range of 127 to
137.degree. C.
In a particular aspect, the subject invention provides a fiber
having a diameter in a range of from 0.1 to 50 denier, a continuous
polymer phase and at least one discontinuous polymer phase which
comprises:
(A) as the at least one discontinuous polymer phase, from about 0.1
percent to about 30 weight percent (by weight of the fiber) of at
least one ethylene polymer having:
i. an I.sub.2 melt index less than or equal to 10 grams/10 minutes,
and
ii. a density of from about 0.85 to about 0.97
grams/centimeters.sup.3, and
(B) as the continuous polymer phase, a polypropylene polymer,
with the proviso that where the ethylene polymer is an
ethylene/.alpha.-olefin interpolymer having an I.sub.2 melt index
in the range of about 5 to about 10 g/10 minutes, the density of
the ethylene/.alpha.-olefin polymer is greater than 0.87 g/cm.sup.3
(or has a DSC percent crystallinity greater than 13 weight
percent), preferably greater than or equal to 0.90 g/cm.sup.3 (or
has a DSC percent crystallinity greater than 33 weight percent) and
more preferably greater than or equal to 0.94 g/cm.sup.3 (or has a
DSC percent crystallinity greater than 60 weight percent),
with the proviso that where the ethylene polymer is an ethylene
homopolymer or ethylene/.alpha.-olefin interpolymer having a
density greater than or equal to 0.94 g/cm3, the I.sub.2 melt index
of the ethylene polymer is less than 5 g/10 minutes,
wherein, prior to any bonding operation, the continuous polymer
phase constitutes more than 50 percent of the fiber surface area
and the two polymer phases cross-sectionally provide an island-sea
configuration, and wherein the fiber thermal bondable at 340
pounds/linear inch and a bond roll surface temperature the range of
127 to 137.degree. C.
In specific embodiments, the discontinuous phase constitutes an
amount of the fiber surface area which is within or less than 50
percent, preferably 25 percent, more preferably 10 percent of
amount contained in the blend composition. That is, in such
embodiments, the surface area percentage of the discontinuous phase
polymer is insubstantial as it closely approximates the total
composition weight percentage of the discontinuous phase polymer),
as determined using an electron microscopy technique which may
include selective staining to enhance resolution.
Preferably, the fiber of the invention will be prepared from a
polymer blend composition comprising:
(A) at least one homogeneously branched ethylene polymer, more
preferably at least one substantially linear
ethylene/.alpha.-olefin interpolymer having:
i. a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63,
ii. a molecular weight distribution, M.sub.w /M.sub.n, defined by
the equation:
and
iii. a critical shear rate at onset of surface melt fracture of at
least 50 percent greater than the critical shear rate at the onset
of surface melt fracture of a linear ethylene polymer having about
the same I.sub.2 and M.sub.W /M.sub.n, and
which constitutes the discontinuous polymer phase, and
(B) at least one isotactic polypropylene propylene.
The subject invention further provides a method for improving the
bonding strength of a fine denier fiber comprised of at least one
polypropylene polymer, the method comprising providing in an
intimate admixture therewith less than or equal to 22 weight
percent, preferably less than or equal to 17 weight percent, more
preferably less than or equal to 12 weight percent of at least one
ethylene polymer having a density of from about 0.85 to about 0.97
g/cm.sup.3 and an I.sub.2 melt index of from about 0.01 to about 10
grams/10 minutes, with the proviso that where the ethylene polymer
is an ethylene/.alpha.-olefin interpolymer having an I.sub.2 melt
index in the range of about 5 to about 10 g/10 minutes, the density
of the ethylene/.alpha.-olefin polymer is greater than 0.87
g/cm.sup.3 and with the proviso that where the ethylene polymer is
an ethylene homopolymer or ethylene/.alpha.-olefin interpolymer
having a density greater than or equal to 0.94 g/cm.sup.3, the
I.sub.2 melt index of the ethylene polymer is less than 5 g/10
minutes.
The subject invention further provides a polymer composition having
improved bond strength comprising:
(A) from about 0.1 percent to about 30 weight percent (by weight of
the composition) of at least one ethylene polymer having:
i. an I.sub.2 melt index less than or equal to 10 grams/1 0
minutes, and
ii. a density of from about 0.85 to 0.97 grams/centimeters.sup.3,
and
(B) a polypropylene polymer,
with the proviso that where the ethylene polymer is an
ethylene/.alpha.-olefin interpolymer having an I.sub.2 melt index
in the range of about 5 to about 10 g/10 minutes, the density of
the ethylene/.alpha.-olefin polymer is greater than 0.87 g/cm.sup.3
and with the proviso that where the ethylene polymer is an ethylene
homopolymer or ethylene/.alpha.-olefin interpolymer having a
density greater than or equal to 0.94 g/cm.sup.3, the I.sub.2 melt
index of the ethylene polymer is less than 5 g/10 minutes.
The subject invention further provides a polymer composition of the
invention, in the form of a fiber, fabric, nonwoven or woven
article, rotomolded article, film layer, injection molded article,
thermoformed article, blow molded article, injection blow molded
article, or extrusion coating composition.
The inventive fibers and fabrics can be produced on conventional
synthetic fiber or fabric processes (e.g., carded staple, spun
bond, melt blown, and flash spun) and they can be used to produce
fabrics having high elongation and tensile strength, without a
significant sacrifice in fiber spinnability. As an unexpected
surprise, the polymer blend exhibits excellent fiber spinnability
even though the ethylene polymer is characterized as having a high
molecular weight. In fact, excellent polymer blend spinnability is
achieved even where the ethylene polymer itself is not spinnable
into fine denier fibers (that is, diameters less than about 50
denier) when used alone.
It is also surprising that improved bond strength is obtained
without commensurate reductions in elongation performance.
It is a further surprise that relative to known PP/HDPE blends,
improved bond strengths are obtained at relatively low polymer
densities and crystallinities.
It is still another surprise that inventive blends based on high
molecular weight ethylene/aromatic vinyl interpolymers provide
dramatically improved bond strengths relative to comparative blends
based on ethylene/.alpha.-olefin interpolymers having comparable
crystallinities and melt indexes.
As another surprise, the invention where the polypropylene polymer
(B) is manufactured using a metallocene or single-site or
constrained geometry catalyst system results in substantially
stable bond strengths at about 340 pli in the bonding temperature
range of from about 127 to about 137.degree. C.
These and other embodiments are more fully described in the
detailed description in conjunction with the following figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a transmission electron microscopy photomicrograph of the
cross-section of an inventive fiber (Inventive Example 1) showing a
continuous polypropylene polymer phase and discontinuous ethylene
polymer (stained dark) phase.
FIG. 2 is a transmission electron microscopy photomicrograph of the
cross-section of an inventive fiber (Inventive Example 3) showing a
continuous polypropylene polymer phase and discontinuous ethylene
polymer (stained dark) phase.
FIG. 3 is a transmission electron microscopy photomicrograph of the
cross-section of an inventive fiber (Inventive Example 9) showing a
continuous polypropylene polymer phase and discontinuous ethylene
polymer (particles with stained dark peripheries) phase.
FIG. 4 is a transmission electron microscopy photomicrograph of the
cross-section of a comparative fiber (comparative example 7)
showing a continuous polypropylene polymer phase and discontinuous
ethylene polymer (stained dark dispersed particles) phase.
FIG. 5 is a transmission electron microscopy (TEM) photomicrograph
of the cross-section of a comparative fiber (comparative example
12) showing a continuous polypropylene polymer phase and
discontinuous ethylene polymer (highly dispersed stained dark
particles) phase.
FIG. 6 is a bar chart illustrating the fabric thermal bond strength
of Inventive Examples 1-3 and comparative example 4.
FIG. 7 is a bar chart illustrating the fabric thermal bond strength
of Inventive Examples 1, 5 and 6 and comparative example 4.
FIG. 8 is a bar chart illustrating the fabric thermal bond strength
of Inventive Examples 1, 8, and 9 and comparative examples 4, 7,
10, 11 and 12.
FIG. 9 is a bar chart illustrating the fabric thermal bond strength
of Inventive Examples 1 and 2 and comparative examples 4, 13, and
14.
FIG. 10 is a bar chart illustrating the fabric thermal bond
strength of Inventive Examples 1 and 6 and comparative examples 4
and 15.
FIG. 11 is a bar chart illustrating the fabric thermal bond
elongation of Inventive Examples 1-3 and comparative example 4.
FIG. 12 is a bar chart illustrating the fabric thermal bond
elongation of Inventive Examples 1, 5 and 6 and comparative example
4.
FIG. 13 is a bar chart illustrating the fabric thermal bond
elongation of Inventive Examples 1, 8, and 9 and comparative
examples 4, 7, 10, 11 and 12.
FIG. 14 is a bar chart illustrating the fabric thermal bond
elongation of Inventive Examples 1 and 2 and comparative examples
4, 13, and 14,
FIG. 15 is a bar chart illustrating the fabric thermal bond
elongation of Inventive Examples I and 6 and comparative examples 4
and 15.
FIG. 16 is a bar chart illustrating the fabric thermal bond
strength of Inventive Examples 16 and 17 and comparative examples
18 and 19.
FIGS. 17a-d are lighted microscope photomicrographs of thermally
bonded inventive fibers (Inventive Example 1) and comparative
fibers (comparative example 4) at 25.times. and 200.times.
magnification.
FIGS. 18a-d are lighted microscope photomicrographs of thermally
bonded inventive fibers (Inventive Example 1) and comparative
fibers (comparative example 4) at 50 .mu.m and 20 .mu.m
magnification.
FIG. 19 is a transmission electron microscopy (TEM) photomicrograph
at 15,000.times. magnification of the bond cross-section of
thermally bonded inventive fibers (Inventive Example 1) showing a
continuous polypropylene polymer phase and a discontinuous ethylene
polymer (stained dark) phase.
FIG. 20 is a transmission electron microscopy (TEM) photomicrograph
at 15,000.times. magnification of the bond cross-section of several
thermally bonded comparative fibers (comparative example 4) showing
stress crazing (stained dark) within the continuous polypropylene
polymer matrix.
DETAILED DESCRIPTION OF THE INVENTION
The term "bonding" as used herein refers to the application of
force or pressure (separate from or in addition to that required or
used to draw fibers to less than or equal to 50 denier) to fuse
molten or softened fibers together such that a bond strength of
greater than or equal to 1,500 grams results.
The term "thermal bonding" is used herein refers to the reheating
of staple fibers and the application of force or pressure (separate
from or in addition to that required or used to draw fibers to less
than or equal to 50 denier) to effect the melting (or softening)
and fusing of fibers such that a bond strength of greater than or
equal to 2,000 grams results. Operations that drawing and fuse
fibers together in a single or simultaneous operation, or prior to
any take-up roll (for example, a godet) such as, for example,
spunbonding are not consider to be a thermal bonding operation,
although the inventive fiber can have the form of or result from a
spunbonding operation and similar fiber making operations.
The terms "visbroken" and "viscracked" are used herein in their
conventional sense to refer to a reactor grade or product
polypropylene polymer which is subsequently cracked or
chain-scissioned prior to, during or by extrusion to provide a
substantially higher melt flow rate. In the present invention, a
viscracked polypropylene polymer will show a MFR change of 3:1,
especially, 5:1 and more especially 7:1 in respect to the ratio of
its subsequent MFR to initial MFR. For example, but the invention
is not limited thereto, a reactor grade polypropylene polymer
having a MFR of 4 can be used in the present invention where it is
visbroken or viscracked to a MFR greater than about 20 (i.e.,
having a >20 visbroken MFR) prior to, during or by extrusion
(for example, in an extruder immediately prior to a spinneret) in a
conventional fiber making operation. In the present invention, to
facilitate visbreaking, an initiator such as a peroxide (for
example, but not limited to, Lupersol.TM. 101) and optionally
antioxidant can be compounded with the initially low MFR
polypropylene polymer prior to fiber making. In one embodiment, the
polypropylene polymer is provided in powder form and the peroxide,
antioxidant and ethylene polymer are admixed via a side-arm
extrusion at the polypropylene polymer manufacturing facility.
Polypropylene polymers having a visbroken melt flow rate are also
referred to in the art as "controlled rheology polypropylene" (see,
e.g., Gessner in U.S. Pat. No. 5,593,768) and initiator-assisted
degraded polypropylene (see, e.g. Polypropylene Handbook, Hanser
Publishers, New York (1996), the disclosure of which is
incorporated by reference).
The term "reactor grade" is used herein in its conventional sense
to refer to a virgin or additive modified polypropylene polymer
which is not cracked or chain-scissioned after its initial
production and as such its MFR will not be substantially changed
during or by extrusion (for example, in an extruder immediately
prior to a spinneret). In the present invention, reactor grade
polypropylene will have MFR change during extrusion of less than
3:1, especially less than or equal to 2:1, more especially less
than or equal to 1.5:1, most especially less than or equal to
1.25:1 with respect to the ratio of the polymer's subsequent MFR to
its initial (before extrusion) MFR. In the present invention,
reactor grade polypropylene polymers characterized as having a
subsequent to initial MFR ratio of less than or equal to 1.25:1
typically contain an effective thermal stabilizer system such as,
for example, but not limited to, 1 total weight percent Irganox.TM.
1010 phenolic antioxidant or Irgafos.TM. 168 phosphite stabilizer
or both. Reactor grade polypropylene polymers characterized as
having a relative low subsequent to initial MFR ratio are referred
to in the art as "constant rheology polypropylene" (see Jezic et
al. U.S. Pat. No. 4,839,228).
The term "excellent spinnability" is used herein to refer to the
ability to produce high quality fine denier fibers using at least
semi-commercial equipment (if not commercial equipment) at at least
semi-commercial production rates (if not commercial production
rates). Representative of excellent spinnability is producing fine
denier fiber at greater than or equal to 750 meters/minute without
any drips using the spinnability test described by Pinoca et al. in
U.S. Pat. No. 5,631,083, the disclosure of which is incorporated
herein by reference.
The term "stable bond strength" is used herein to mean that the
thermal bond strength for the fabricated article (e.g. fiber) is in
the range of 4,000 to 6,000 grams as determined at about 340 pli
and bonding temperatures in the range of 127-137.degree. C.
The term "fine denier fiber" is used herein to refer to fibers
having a diameter less than or equal to 50 denier.
The polymer blend composition used to make the fiber and fabric of
the present invention comprises at least one polypropylene polymer
preferably a crystalline polypropylene polymer. The polypropylene
polymer can be coupled, branched, visbroken or a reactor grade
resin. The inventive composition comprises from about 70 to about
99.9 weight percent of at least one polypropylene polymer. In
certain embodiments, inventive composition comprises equal to or
greater than 78 weight percent, especially equal to or greater than
83 weight percent and more especially equal to or greater than 88
weight percent of at least one polypropylene polymer.
A crystalline polypropylene polymer is a polymer with at least
about 90 mole percent of its repeating units derived from
propylene, preferably at least about 97 percent, more preferably at
least about 99 percent. The term "crystalline" is used herein to
mean isotactic polypropylene having at least about 93 percent
isotactic triads as measured by .sup.13 C NMR, preferably at least
about 95 percent, more preferably at least about 96 percent.
The polypropylene polymer comprises either homopolymer
polypropylene or propylene polymerized with one or more other
monomers addition polymerizable with propylene. The other monomers
are preferably olefins, more preferably alpha olefins, most
preferably ethylene or an olefin having a structure RCH=CH.sub.2
where R is aliphatic or aromatic and has at least two and
preferably less than about 18 carbon atoms. Hydrocarbon olefin
monomers within the skill in the art, include hydrocarbons having
one or more double bonds at least one of which is polymerizable
with the alpha olefin monomer.
Suitable alpha olefins for polymerizing with propylene include 1
-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene,
1-unidecene, 1-dodecene and the like as well as 4-methyl-1-pentene,
4-methyl-1-hexene, 5-methyl-1-hexene, vinylcyclohexane, styrene and
the like. The preferred alpha olefins include ethylene, 1-butene,
1-hexene, and 1-octene.
Optionally, but not in the most preferred embodiment of the present
invention, the polypropylene polymer comprises monomers having at
least two double bonds which are preferably dienes or trienes.
Suitable diene and triene comonomers include
7-methyl-1,6-octadiene, 3,7-dimethyl-1,6-octadiene,
5,7-dimethyl-1,6-octadiene, 3,7,11-trimethyl-1,6,10-octatriene,
6-methyl-1,5-heptadiene, 1,3-butadiene, 1,6-heptadiene,
1,7-octadiene, 1,8-nonadiene, 1,9-decadiene, 1,10-undecadiene,
norbornene, tetracyclododecene, or mixtures thereof, preferably
butadiene, hexadienes, and octadienes, most preferably
1,4-hexadiene, 1,9-decadiene, 4-methyl-1,4-hexadiene,
5-methyl-1,4-hexadiene, dicyclopentactiene, and
5-ethylidene-2-norbornene.
Suitable polypropylenes are formed by means within the skill in the
art, for example, using single site catalysts or Ziegler Natta
catalysts. The propylene and optional alpha-olefin monomers are
polymerized under conditions within the skill in the art, for
instance as disclosed by Galli, et al., Angew. Macromol. Chem.,
Vol. 120, 73 (1984), or by E. P. Moore, et al. in Polypropylene
Handbook, Hanser Publishers, New York, 1996, particularly pages
11-98, the disclosures of which are incorporated herein by
reference.
The polypropylene polymer used in the present invention is suitably
of any molecular weight distribution (MWD). Polypropylene polymers
of broad or narrow MWD are formed by means within the skill in the
art. For fiber applications, generally a narrower MWD is preferred
(for example, a M.sub.w /M.sub.n ratio or polydispersity of less
than or equal to 3). Polypropylene polymers having a narrow MWD can
be advantageously provided by visbreaking or by manufacturing
reactor grades (non-visbroken) using single-site catalysis or
both.
Polypropylene polymers for use in the present invention preferably
have a weight average molecular weight as measured by gel
permeation chromatography (GPC) greater than about 100,000,
preferably greater than about 115,000, more preferably greater than
about 150,000, most preferably greater than about 250,000 to obtain
desirably high mechanical strength in the final product.
Preferably, the polypropylene polymer has a melt flow rate (MFR) in
the range of about 1 to about 1000 grams/10 minutes, more
preferably in range of about 5 to about 100 grams/10 minutes, as
measured in accordance with ASTM D1238 at 230.degree. C./2.16
kg.
In general, for fiber making, especially fiber spinning, the melt
flow rate of the polypropylene polymer is preferably greater than
or equal to 20 g/10 minutes, more preferably greater than or equal
to 25 g/10 minutes, and especially in the range of from about 25 to
about 50 g/10 minutes, most especially from about 30 to about 40
g/10 minutes.
But specifically for staple fiber, the melt flow rate (MFR) of the
polypropylene polymer is preferably in the range of about 10 to
about 20 g/10 minutes. For spunbond fiber, the melt flow rate (MFR)
of the polypropylene polymer is preferably in the range of about 20
to about 40 g/10 minutes. For melt blown fiber, the melt flow rate
(MFR) of the polypropylene polymer is preferably in the range of
about 500 to about 1500 g/10 minutes. For gel spun fiber, the melt
flow rate (MFR) of the polypropylene polymer is preferably less
than or equal to 1 g/10 minutes.
The polypropylene polymer used in the present invention can be
branched or coupled to provide increased nucleation and
crystallization rates. The term "coupled" is used herein to refer
to polypropylene polymers which are rheology-modified such that
they exhibit a change in the resistance of the molten polymer to
flow during fiber making operation (for example, in the extruder
immediately prior to the spinneret in a fiber spinning operation.
Whereas "visbroken" is in the direction of chain-scission,
"coupled" is in the direction of crosslinking or networking. An
example of coupling is where a couple agent (for example, an azide
compound) is added to a relatively high melt flow rate
polypropylene polymer such that after extrusion the resultant
polypropylene polymer composition attains a substantially lower
melt flow rate than the initial melt flow rate. For the coupled or
branched polypropylene used in the present invention the ratio of
subsequent MFR to initial MFR is preferably less than or equal to
0.7:1, more preferably less than or equal to 0.2:1.
Suitable branched polypropylene for use in the present invention is
commercially available for instance from Montell North America
under the trade designations Profax PF-611 and PF-814.
Alternatively, suitable branched or coupled polypropylene can be
prepared by means within the skill in the art such as by peroxide
or electron-beam treatment, for instance as disclosed by DeNicola
et al. in U.S. Pat. No. 5,414,027 (the use of high energy
(ionizing) radiation in a reduced oxygen atmosphere); EP 0 190 889
to Himont (electron beam irradiation of isotactic polypropylene at
lower temperatures); U.S. Pat. No. 5,464,907 (Akzo Nobel NV); EP 0
754 711 Solvay (peroxide treatment); and U.S. patent application
Ser. No. 09/133,576, filed August 13, 1998 (azide coupling agents);
the disclosures of all of which are incorporated herein by
reference.
All references herein to elements or metals belonging to a certain
Group refer to the Periodic Table of the Elements published and
copyrighted by CRC Press, Inc., 1989. Also any reference to the
Group or Groups shall be to the Group or Groups as reflected in
this Periodic Table of the Elements using the. IUPAC system for
numbering groups.
Preparation of crystalline polypropylene polymers is well within
the skill, in the art. Advantageous catalysts for use in preparing
narrow molecular weight distribution polypropylene polymers useful
in the practice of the invention are preferably derivatives of any
transition metal including Lanthanides, but preferably of Group 3,
4, or Lanthanide metals which are in the +2, +3, or +4 formal
oxidation state. Preferred compounds include metal complexes
containing from 1 to 3 .PI.-bonded anionic or neutral ligand
groups, which are optionally cyclic or non-cyclic delocalized
.PI.-bonded anionic ligand groups. Exemplary of such .PI.-bonded
anionic ligand groups are conjugated or nonconjugated, cyclic or
non-cyclic dienyl groups, and allyl groups. By the term
".PI.-bonded" is meant that the ligand group is bonded to the
transition metal by means of its delocalized .PI.-electrons.
Each atom in the delocalized n-bonded group is optionally
independently substituted with a radical selected from the group
consisting of hydrogen, halogen, hydrocarbyl, halohydrocarbyl,
hydrocarbyl-substituted metalloid radicals wherein the metalloid is
selected from Group 14 of the Periodic Table of the Elements, and
such hydrocarbyl- or hydrocarbyl-substituted metalloid radicals
further substituted with a Group 15 or 16 hetero atom containing
moiety. Included within the term "hydrocarbyl" are C.sub.1
-C.sub.20 straight, branched and cyclic alkyl radicals, C.sub.6
-C.sub.20 aromatic radicals, C.sub.7 -C.sub.20 alkyl-substituted
aromatic radicals, and C.sub.7 -C.sub.20 aryl-substituted alkyl
radicals. In addition two or more such adjacent radicals may
together form a fused ring system, a hydrogenated fused ring
system, or a metallocycle with the metal.
Suitable hydrocarbyl-substituted organometalloid radicals include
mono-, di- and tri-substituted organometalloid radicals of Group 14
elements wherein each of the hydrocarbyl groups contains from 1 to
20 carbon atoms. Examples of advantageous hydrocarbyl-substituted
organometalloid radicals include trimethylsilyl, triethylsilyl,
ethyldimethylsilyl, methyldiethylsilyl, triphenylgermyl, and
trimethylgermyl groups. Examples of Group 15 or 16 hetero atom
containing moieties include amine, phosphine, ether or thioether
moieties or monovalent derivatives thereof, e. g. amide, phosphide,
ether or thioether groups bonded to the transition metal or
Lanthanide metal, and bonded to the hydrocarbyl group or to the
hydrocarbyl- substituted metalloid containing group.
Examples of advantageous anionic, delocalized .PI.-bonded groups
include cyclopentadienyl, indenyl, fluorenyl, tetrahydroindenyl,
tetrahydrofluorenyl, octahvdrofluorenyl, pentadienyl,
cyclohexadienyl, dihvdroanthracenyl, hexahydroanthracenyl, and
decahydroanthracenyl groups, as well as C.sub.1 -C.sub.10
hydrocarbyl-substituted or C.sub.1 -C.sub.10
hydrocarbyl-substituted silyl substituted derivatives thereof.
Preferred anionic delocalized .PI.-bonded groups are
cyclopentaclienyl, pentamethylcyclopentadienyl,
tetramethylcyclopentadienvi, tetramethylsilvlcyclopentadienyl,
indenyl, 2,3dimethylindenyl, fluorenyl, 2-methylindenvi,
2-methyl-4-phenytindenyl, tetrahydrofluorenvi, octahvdrofluorenyl,
and tetrahydroindenyl.
A preferred class of catalysts are transition metal complexes
corresponding to the Formula A:
or a dimer thereof
wherein:
L is an anionic, delocalized, n-bonded group that is bound to M,
containing up to 50 non-hydrogen atoms, optionally two L groups may
be joined together forming a bridged structure, and further
optionally one L is bound to X;
M is a metal of Group 4 of the Periodic Table of the Elements in
the +2, +3 or +4 formal oxidation state;
X is an optional, divalent substituent of up to 50 non-hydrogen
atoms that together with L forms a metallocycle with M;
X' at each occurrence is an optional neutral Lewis base having up
to 20 non-hydrogen atoms and optionally one X'0 and one L may be
joined together;
X" each occurrence is a monovalent, anionic moiety having up to 40
non-hydrogen atoms, optionally, two X" groups are covalently bound
together forming a divalent dianionic moiety having both valences
bound to M, or, optionally two X" groups are covalently bound
together to form a neutral, conjugated or nonconjugated diene that
is n-bonded to M (whereupon M is in the +2 oxidation state), or
further optionally one or more X" and one or more X' groups are
bonded together thereby forming a moiety that is both covalently
bound to M and coordinated thereto by means of Lewis base
functionality;
l is 0, 1 or 2;
m is 0 or 1;
n is a number from 0 to 3;
p is an integer from 0 to 3, and
the sum, l+m+p, is equal to the formal oxidation state of M, except
when two X" groups together form a neutral conjugated or
non-conjugated diene that is .PI.-bonded to M, in which case the
sum l+m is equal to the formal oxidation state of M.
Preferred complexes include those containing either one or two L
groups.
The latter complexes include those containing a bridging group
linking the two L groups. Preferred bridging groups are those
corresponding to the formula (ER*.sub.2).sub.x wherein E is
silicon, germanium, tin, or carbon, R* independently each
occurrence is hydrogen or a group selected from silyl, hydrocarbyl,
hydrocarbyloxy and combinations thereof, said R* having up to 30
carbon or silicon atoms, and x is 1 to 8. Preferably, R*
independently each occurrence is methyl, ethyl, propyl, benzyl,
tert-butyl, phenyl, methoxy, ethoxy or phenoxy.
Examples of the complexes containing two L groups are compounds
corresponding to the formula: ##STR1##
wherein:
M is titanium, zirconium or hafnium, preferably zirconium or
hafnium; in the +2 or +4 formal oxidation state;
R.sup.3 in each occurrence independently is selected from the group
consisting, of hydrogen, hydrocarbyl, silyl, germyl, cyano, halo
and combinations thereof, said R.sup.3 having up to 20 non-hydrogen
atoms, or adjacent R.sup.3 groups together form a divalent
derivative (e.g., a hydrocarbadiyl, germadiyl group) thereby
forming a fused ring system, and V independently each occurrence is
an anionic ligand group of up to 40 non-hydrogen atoms, or two X"
groups together form a divalent anionic ligand group of up to 40
non-hydrogen atoms or together are a conjugated diene having from 4
to 30 non-hydrogen atoms forming .alpha.-complex with M, whereupon
M is in the +2 formal oxidation state, and R*, E and x are as
previously defined.
The foregoing metal complexes are especially suited for the
preparation of polymers having stereoregular molecular structure.
In such capacity it is preferred that the complex possesses C.sub.s
symmetry or possesses a chiral, stereorigid structure. Examples of
the first type are compounds possessing different delocalized
.PI.-bonded systems, such as one cyclopentadienyl group and one
fluorenyl group. Similar systems based on Ti(IV) or Zr(IV) were
disclosed for preparation of syndiotactic olefin polymers in Ewen,
et al., J. Am. Chem. Soc., 110, pp. 6255-6256 (1980), incorporated
herein by reference. Examples of chiral structures include rac
bis-indenyl complexes. Similar systems based on Ti(IV) or Zr(IV)
were disclosed for preparation of isotactic olefin polymers in Wild
et al., J. Organomet. Chem., 232, pp. 233-47, (1982), incorporated
herein by reference.
Suitable bridged ligands containing two n-bonded groups are:
(dimethylsilyl-bis(cyclopentadienyl)),
(dimethylsilyl-bis(methylcyclopentadienyl)),
(dimethylsilyl-bis(ethylcyclopentadienyl)),
(dimethylsilyl-bis(t-butylcyclopentadienyl)),
(dimethylsilyl-bis(tetramethylcyclopentadienyl)),
(dimethylsilyl-bis(indenyl)),
(dimethylsilyl-bis(tetrahydroindenyl)),
(dimethylsilyl-bis(fluorenyl)),
(dimethylsilyl-bis(tetrahydrofluorenyl)),
(dimethylsilyl-bis(2-methyl-4-phenylindenyl)),
(dimethylsilyl-bis(2-methylindenyl)),
(dimethylsilyl-cyclopentadienyl-fluorenyl),
(dimethylsilyl-cyclopentadienyl-octahydrofluorenyl),
(dimethylsilyl-cyclopentadienyl-tetrahydrofluorenyl),
(1,1,2,2-tetramethyl-1,2-disilyl-bis-cyclopentadienyl),
(1,2-bis(cyclopentadienyl)ethane, and
(isopropylidene-cyclopentadienyl-fluorenyl).
Preferred X" groups are selected from hydride, hydrocarbyl, silyl,
germyl, halohydrocarbyl, halosilyl, silyl hydrocarbyl and
aminohydrocarbyl groups, or two X" groups together form a divalent
derivative of a conjugated diene or else together they form a
neutral, .PI.-bonded, conjugated diene. Most preferred X" groups
are C.sub.1 -C.sub.20 hydrocarbyl groups, including those
optionally formed from two X" groups together.
A further class of metal complexes corresponds to the preceding
formula L.sub.l MX.sub.m X'.sub.n X".sub.p, or a dimer thereof,
wherein X is a divalent substituent of up to 50 non-hydrogen atoms
that together with. L forms a metallocycle with M.
Preferred divalent X substituents include groups containing up to
30 non-hydrogen atoms comprising at least one atom that is oxygen,
sulfur, boron or a member of Group 14 of the Periodic Table of the
Elements directly attached to the delocalized .PI.-bonded group,
and a different atom, selected from the group consisting of
nitrogen, phosphorus, oxygen or sulfur that is covalently bonded to
M.
A preferred class of such Group 4 metal coordination complexes
corresponds to the formula: wherein: ##STR2##
wherein:
M is titanium, zirconium or hafnium in the +2, +3 or +4 formal
oxidation state;
X" and R.sup.3 are as previously defined for formulas Al and
All;
Y is --O--, --S--, --NR*--, --NR*.sub.2 --, or --PR*--; and
Z is SiR*.sub.2, CR*.sub.2, SiR*.sub.2 SiR*.sub.2, CR*.sub.2
CR*.sub.2, CR*.dbd.CR*, CR*.sub.2 SiR*.sub.2, or GeR*.sub.2,
wherein R* is as previously defined.
Illustrative Group 4 metal complexes that are optionally used as
catalysts include:
cyclopentadienyltitaniumtrimethyl,
cyclopentadienyltitaniumtriethyl,
cyclopentadienyltitaniumtriisopropyl,
cyclopentadienyltitaniumtriphenyl,
cyclopentadienyltitaniumtribenzyl,
cyclopentadienyltitanium-2,4-dimethylpentadienyl,
cyclopentadienyltitanium-2,4-dimethvlpentadienyltriethylphosphine,
cyclopentadienyltitanium-2,4-dimethvlpentadienyltriethylphosphine,
cyclopentadienyltitaniumdimethylmethoxide,
cyclopentadienyltitaniumdimethylchloride,
pentamethylcyclopentadienyltitaniumtrimethyl,
indenyltitaniumtrimethyl, indenyltitaniumtriethyl,
indenyltitaniumtripropyl, indenyltitaniumtriphenyl,
tetrahydroindenyltitaniumtribenzyl,
pentamethylcyclopentadienyltitaniumtriisopropyl,
pentamethylcyclopentadienyltitaniumtribenzyl,
pentamethylcyclopentadienyltitaniumdimethylmethoxide,
pentamethylcyclopentadienyltitaniumdimethylchloride,
bis(.eta.5-2,4-dimethylpentadienyl) titanium,
bis(.eta.5-2,4-dimethylpentadienyl)titaniumtrimethylphosphine,
bis(.eta.5-2,4-dimethylpentadienyl)titaniumtriethylphosphine,
octahydrofluorenyltitaniumtrimethyl,
tetrahydroindenyltitaniumtrimethyl,
tetrahydrofluorenyltitaniumtrimethyl,
(tert-butylamido)(1,1-dimethyl-2,3,4,9,10--1,4,.eta.5,6,7,8-hexahydronapht
halenyl)dimethylsilanetitaniumdimethyl,
(tert-butylamido)(1,1,2,3-tetramethyl-2,3,4,9,10--1,4,5,6,7,8-hexahydronap
hthalenyl)dimethylsilanetitaniumdimethyl,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethylsilanetitani
um dibenzyl,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethylsilanetitani
um dimethyl,
(tert-butylamido)(tetramethyl-,.eta.5-cyclopentadienyl)-1,2-ethanediyltita
nium dimethyl,
(tert-butylamido)(tetramethyl-.eta.5-indenyl)dimethylsilanetitanium
dimethyl,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethylsilane
titanium (III) 2-(dimethylamino)benzyl;
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethylsilanetitani
um (III) allyl,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethylsilanetitani
um (III) 2,4-dimethylpentadienyl,
(tert-butylamido)(tetramethyl-,.eta.5-cyclopentadienyl)dimethyl-silanetita
nium (II)1,4-diphenyl-1,3-butadiene,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethyl-silanetitan
ium (II)1,3-pentadiene,
(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (II)
1,4-diphenyl-1,3-butadiene,
(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (II)
2,4-hexadiene,
(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (IV)
2,3-dimethyl-1,3-butadiene,
(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium
(IV)isoprene,
(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium
1,3-butadiene,
(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium (IV)
2,3-dimethyl-1,3-butadiene,
(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium (IV)
isoprene;
(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium (IV)
dimethyl;
(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium (IV)
dibenzyl;
(tert-butylamido)(2,3dimethylindenyl)dimethylsilanetitanium
1,3-butadiene,(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium
(11) 1,3-pentadiene,
(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium (11)
1,4-diphenyl-1,3-butadiene,
(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (11)
1,3-pentadiene,(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium
(IV) dimethyl,
(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (IV)
dibenzyl,
(tert-butylamido)(2-methyl-4-phenylindenyl)dimethylsilanetitanium
(II) 1,4-diphenyl-1,3-butadiene,
(tert-butylamido)(2-methyl-4-phenylindenyl)dimethylsilanetitanium
(II) 1,3-pentadiene,
(tert-butylamido)(2-methyl-4-phenylindenyl)dimethylsilanetitanium
(II) 2,4-hexadiene,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethyl-silanetitan
ium 1,3-butadiene,
(tert-butylamido)(tetramethyl-il5-cyclopentadienyl)dimethyl-silanetitanium
(IV) 2,3-dimethyl-1,3-butadiene,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethyl-silanetitan
ium (IV) isoprene,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethyl-silanetitan
ium (II) 1,4-dibenzyl-1,3-butadiene,
(tert-butylamido)(tetramethyl-,.eta.5-cyclopentadienyl)dimethyl-silanetita
nium (II) 2,4-hexadiene,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl)dimethyl-silanetitan
ium (II) 3-methyl-1,3-pentadiene,
(tert-butylamido)(2,4-dimethylpentadien-3-yl)dimethyl-silanetitaniumclimet
hyl,
(tert-butylamido)(6,6dimethylcyclohexadienyl)dimethyl-silanetitaniumdimeth
yl,
(tert-butylamido)(1,1-dimethyl-2,3,4,9,10,1,4,5,6,7,8-hexahydronaphthalen4
-yl)dimethylsilanetitaniumdimethyl,
(tert-butylamido)(1,1,2,3-tetramethyl-2,3,4,9,10,1,4,5,6,7,8-hexahydronaph
thalen4-yl)dimethylsilanetitaniumdimethyl(tert-butylamido)(tetramethyl-.eta
.5-cyclopentadienyl methylphenyl-silanetitanium (IV) dimethyl,
(tert-butylamido)(tetramethyl-.eta.5-cyclopentadienyl
methylphenyl-silanetitanium (II) 1,4-diphenyl-1,3-butadiene,
1-(tert-butylamido)-2-(tetramethyl-.eta.5-cyclopentadienyl)ethanediyl-tita
nium (IV) dimethyl, and
1-(tert-butylamido)-2-(tetramethyl-.eta.5-cyclopentadienyl)ethanediyl-tita
nium (II) 1,4-diphenyl-1,3-butadiene.
Complexes containing two L groups including bridged complexes
include:
bis(cyclopentadienyl)zirconiumdimethyl,
bis(cyclopentadienyl)zirconium dibenzyl,
bis(cyclopentadienyl)zirconium methyl benzyl,
bis(cyclopentadienyl)zirconiummethyl phenyl,
bis(cyclopentadienyl)zirconiumdiphenyl,
bis(cyclopentadienyl)titanium-allyl,
bis(cyclopentadienyl)zirconiummethylmethoxide,
bis(cyclopentadienyl)zirconiummethylchloride,
bis(pentamethylcyclopentadienyl)zirconiumdime ethyl,
bis(pentamethylcyclopentadienyl)titaniumdimethyl,
bis(indenyl)zirconiumdimethyl, bis(indenyl)zirconiummethyl
(2-(dimethylamino)benzyl), bis(indenyl)zirconium
methyltrimethylsilyl, bis(tetrahydroindenyl)zirconium
methyltrimethylsilyl,
bis(pentamethylcyclopentadienyl)zirconiummethyl benzyl,
bis(pentamethylcyclopentadienyl)zirconiumdibenzyl,
bis(pentamethylcyclopentadienyl)zirconiummethylmethoxide,
bis(pentamethylcyclopentadienyl)zirconiummethvylchloride,
bis(methylethylcyclopentadienyl)zirconiumdimethyl,
bis(butylcyclopentadienyl)zirconium dibenzyl,
bis(t-butylcyclopentadienyl)zirconiumdimethyl,
bis(ethyltetramethylcyclopentadienyl)zirconiumdimethyl,
bis(methylpropylcyclopentadienyl)zirconium dibenzyl,
bis(trimethylsilylcyclopentadienyl)zirconium dibenzyl,
dimethylsilyl-bis(cyclopentadienyl)zirconiumdimethyl,
dimethylsilyl-bis(tetramethylcyclopentadienyi)titanium-(III)allyl
dimethylsilyl-bis(t-butylcyclopentadienyl)zirconiumdichloride,
dimethylsilyl-bis(n-butylcyclopentadienyl)zirconiumdichloride,
(methylene-bis(tetramethylcyclopentadienyl)titanium(III)
2-(dimethylamino)benzyl,
(methylene-bis(n-butylcyclopentadienyl)titanium(III)
2-(dimethylamino)benzyl,
dimethylsilyl-bis(indenyl)zirconiumbenzylchloride,
dimethylsilyl-bis(2-methylindenyl)zirconiumdimethyl,
dimethylsilyl-bis(2-methyl-4-phenylindenyl)zirconiumdimethyl,
dimethylsilyl-bis(2-methylindenyl)zirconium-1,4-diphenyl-1,3-butadiene,
dimethylsilyl-bis(2-methyl-4-phenylindenyl)zirconium (II)
1,4-diphenyl-1,3-butadiene,
dimethylsilyl-bis(tetrahydroindenyl)zirconium(II)
1,4-diphenyl-1,3-butadiene,
dimethylsilyl-bis(fluorenyl)zirconiummethylchloride,
dimethylsilyl-bis(tetrahydrofluorenyl)zirconium
bis(trimethylsilyl), and
dimethylsilyl(tetramethylcyclopentadienyi)(fluorenyl)zirconium
dimethyl.
Other catalysts, especially catalysts containing other Group 4
metals, will, of course, be apparent to those skilled in the
art.
Preferred metallocene species include constrained geometry metal
complexes, including titanium complexes, and methods for their
preparation as are disclosed in U.S. application Ser. No. 545,403,
filed Jul. 3,1990 (EP-A416,815); U.S. application Ser. No. 967,365,
filed Oct. 28, 1992 (EP-A-514,828); and U.S. application Ser. No.
876,268, filed May 1, 1992, (EP-A-520,732), as well as U.S. Pat.
Nos. 5,055,438; 5,057,475; 5,096,867; 5,064,802; 5,096,867;
5,132,380; 5,132,380; 5,470,993; 5,486,632; 5,132,380; and
5,321,106. The teachings of all the foregoing patents, publications
and patent applications is hereby incorporated by reference in
their entireties.
Metallocene catalysts are advantageously rendered catalytically
active by combination with one or more activating cocatalysts, by
use of an activating technique, or a combination thereof.
Advantageous cocatalysts are those boron-containing cocatalysts
within the skill in the art. Among the boron-containing cocatalysts
are tri(hydrocarbyl)boron compounds and halogenated derivatives
thereof, advantageously having from 1 to about 10 carbons in each
hydrocarbyl or halogenated hydrocarbyl group, more especially
perfluorinated tri(aryl)boron compounds, and most especially
tris(pentafluorophenyl)borane), amine, phosphine, aliphatic alcohol
and mercaptan adducts of halogenated tri(C.sub.1 -C.sub.10
hydrocarbyl)boron compounds, especially such adducts of
perfluorinated tri(aryl)boron compounds. Alternatively, the
cocatalyst includes borates such as tetrapheny Borate having as
counterions ammonium ions such as are within the skill in the art
as illustrated by European Patent EP 672,688 (Canich, Exxon),
published Sep. 20, 1995.
The cocatalyst can be used in combination with a
tri(hydrocarbyl)aluminum compound having from 1 to 10 carbons in
each hydrocarbyl group or an oligomeric or polymeric alumoxane. It
is possible to employ these aluminum compounds for their beneficial
ability to scavenge impurities such as oxygen, water, and aldehydes
from the polymerization mixture. Preferred aluminum compounds
include trialkyl aluminum compounds having from 2 to 6 carbons in
each alkyl group, especially those wherein the alkyl groups are
ethyl, propyl, isopropyl, n-butyl, isobutyl, pentyl, neopentyl, or
isopentyl, and methylalumoxane, modified by methylalumoxane (that
is methylalumoxane modified by reaction with triisobutyl aluminum)
(MMAO) and diisobutylalumoxane. The molar ratio of aluminum
compound to metal complex is preferably from 1:10,000 to 1000:1,
more preferably from 1:5000 to 100:1, most preferably from 1:100 to
100:1.
Cocatalysts; are used in amounts and under conditions within the
skill in the art. Their use is applicable to all processes within
the skill in the art, including solution, slurry, bulk (especially
propylene), and gas phase polymerization processed. Such processes
include those fully disclosed in the references cited
previously.
The molar ratio of catalyst/cocatalyst or activator employed
preferably ranges from about 1:10,000 to about 100:1, more
preferably from about 1:5000 to about 10:1, most preferably from
about 1:1000 to about 1:1.
When utilizing such strong Lewis acid cocatalysts; to polymerize
higher (.alpha.-olefins, especially propylene, it has been found
especially desirable to also contact the catalyst/cocatalyst
mixture with a small quantity of ethylene or hydrogen (preferably
at least one mole of ethylene or hydrogen per mole of metal
complex, suitably from 1 to 100,000 moles of ethylene or hydrogen
per mole of metal complex). This contacting may occur before, after
or simultaneously to contacting with the higher .alpha.-olefin. If
the foregoing Lewis acid activated catalyst compositions are not
treated in the foregoing manner, either extremely long induction
periods are encountered or no polymerization at all results. The
ethylene or hydrogen may be used in a suitably small quantity such
that no significant affect on polymer properties is observed.
In most instances, the polymerization advantageously takes place at
conditions known in the prior art for Ziegler-Natta or
Kaminsky-Sinn type polymerization reactions, i.e., temperatures
from 0-250.degree. C. and pressures from atmospheric to 3000
atmospheres. Suspension, solution, slurry, gas phase or high
pressure, whether employed in batch or continuous form or under
other process conditions, including the recycling of condensed
monomers or solvent, may be employed if desired. Examples of such
processes are well known in the art for example, WO 88/02009-A1 or
U.S. Pat. No. 5,084,534 (both incorporated herein by reference),
disclose conditions that are advantageously employed with the
polymerization catalysts and are incorporated herein by reference
in their entireties. A support, especially silica, alumina, or a
polymer (especially polytetrafluoroethylene or a polyolefin) is
optionally employed, and desirably is employed when the catalysts
are used in a gas phase polymerization process. Such supported
catalysts are advantageously not affected by the presence of liquid
aliphatic or aromatic hydrocarbons such as are optionally present
under the use of condensation techniques in a gas phase
polymerization process. Methods for the preparation of supported
catalysts are disclosed in numerous references, examples of which
are U.S. Pat. Nos. 4,808,561; 4,912,075; 5,008,228; 4,914,253; and
5,086,025 (all incorporated herein by reference) and are suitable
for the preparation of supported catalysts.
In such a process the reactants and catalysts are optionally added
to the solvent sequentially, in any order, or alternatively one or
more of the reactants or catalyst system components are premixed
with solvent or material preferably miscible therewith then mixed
together or into more solvent optionally containing the other
reactants or catalysts. The preferred process parameters are
dependent on the monomers used and the polymer desired.
Propylene is added to the reaction vessel in predetermined amounts
to achieve predetermined per ratios, advantageously in gaseous form
using a joint mass flow controller. Alternatively propylene or
other liquid monomers are added to the reaction vessel in amounts
predetermined to result in ratios desired in the final product.
They are optionally added together with the solvent (if any),
alpha-olefin and functional comonomer, or alternatively added
separately. The pressure in the reactor is a function of the
temperature of the reaction mixture and the relative amounts of
propylene and/or other monomers used in the reaction.
Advantageously, the polymerization process is carried out at a
pressure of from about 10 to about 1000 psi (70 to 7000 kPa), most
preferably from about 140 to about 550 psi (980 to 3790 kPa). The
polymerization is then conducted at a temperature of from 25 to
200.degree. C., preferably from 50 to 100.degree. C., and most
preferably from 60 to 80.degree. C.
The process is advantageously continuous, in which case the
reactants are added continuously or at intervals and the catalyst
and, optionally cocatalyst, are added as needed to maintain
reaction or make up loss or both.
Solution polymerization or bulk polymerization is preferred. In the
latter case liquid polypropylene is the reaction medium. Preferred
solvents include mineral oils and the various hydrocarbons which
are liquid at reaction temperatures. Illustrative examples of
useful solvents include straight- and branched-chain hydrocarbons
such as alkanes, e.g. isobutane, butane, pentane, isopentene,
hexane, heptane, octane and nonane, as well as mixtures of alkanes
including kerosene and Isopar E, available from Exxon Chemicals
Inc.; cyclic and alicyclic hydrocarbons such as cyclopentane,
cyclohexane, methylcyclohexane, methylcycloheptane, and mixtures
thereof; and aromatics and alkyl-substituted aromatic compounds
such as benzene, toluene, xylenes, ethylbenzene, diethylbenzene,
and the like; and perfluorinated hydrocarbons such as
perfluorinated C.sub.4 -C.sub.10 alkanes. Suitable solvents may
include liquid olefins which may act as monomers or comonomers.
Mixtures of the foregoing are also suitable.
At all times, the individual ingredients as well as the recovered
catalyst components are protected from oxygen and moisture.
Therefore, the catalyst components and catalysts are prepared and
recovered in an oxygen- and moisture-free atmosphere. Preferably,
therefore, the reactions are performed in the presence of a dry,
inert gas such as, for example, nitrogen.
Without limiting in any way the scope of the invention, one means
for carrying out such a polymerization process is as follows. In a
stirred-tank reactor, olefin monomer is introduced continuously
together with solvent and polyene monomer. The reactor contains a
liquid phase composed substantially of monomers together with any
solvent or additional diluent. Catalyst and cocatalyst are
continuously introduced in the reactor liquid phase. The reactor
temperature and pressure may be controlled by adjusting the
solvent/monomer ratio, the catalyst addition rate, as well as by
cooling or heating coils, jackets or both. The polymerization rate
is controlled by the rate of catalyst addition. The polymer product
molecular weight is controlled, optionally, by controlling other
polymerization variables such as the temperature, monomer
concentration, or by a stream of hydrogen introduced to the
reactor, as is well known in the art. The reactor effluent is
contacted with a catalyst kill agent such as water or an alcohol.
The polymer solution is optionally heated, and the polymer product
is recovered by flashing off gaseous monomers as well as residual
solvent or diluent at reduced pressure, and, if necessary,
conducting further devolatilization in equipment such as a
devolatilizing extruder. In a continuous process, the mean
residence time of the catalyst and polymer in the reactor generally
is from about 5 minutes to 8 hours, and preferably from 10 minutes
to 6 hours.
Preferably, the polymerization is conducted in a continuous
solution polymerization system, optionally comprising more than one
reactor connected in series or parallel.
The ethylene polymer used in the polymer blend composition to make
the fiber and fabric of the present invention is characterized as
having a high molecular weight. Suitable ethylene polymers include,
for example, high density polyethylene (HDPE), heterogeneously
branched linear low density polyethylene (LLDPE), heterogeneously
branched ultra low density polyethylene (ULDPE), homogeneously
branched linear ethylene polymers, homogeneously branched
substantially linear ethylene polymers, homogeneously branched long
chain branched ethylene polymers, and ethylene vinyl or vinylidene
aromatic monomer interpolymers. But homogeneously branched ethylene
polymers and ethylene vinyl or vinylidene aromatic monomer
interpolymers are preferred, and homogeneously branched
substantially linear ethylene polymers and substantially random
ethylene/vinyl aromatic interpolymers are most preferred.
The homogeneously branched substantially linear ethylene polymers
used in the polymer blend compositions disclosed herein can be
interpolymers of ethylene with at least one C.sub.3 -C.sub.20
.alpha.-olefin. The term "Interpolymer" and "ethylene polymer" used
herein indicates that the polymer can be a copolymer, a terpolymer.
Monomers usefully copolymerized with ethylene to make the
homogeneously branched linear or substantially linear ethylene
polymers include the C.sub.3 -C.sub.20 .alpha.-olefin especially
1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Especially
preferred comonomers include I-pentene, I-hexene and 1-octene.
Copolymers of ethylene and a C.sub.3 -C.sub.20 .alpha.-olefin are
especially preferred.
The term "substantially linear" means that the polymer backbone is
substituted with 0.01 long chain branches/1000 carbons to 3 long
chain branches/1000 carbons, more preferably from 0.01 long chain
branches/1000 carbons to I long chain branches/1000 carbons, and
especially from 0.05 long chain branches/1000 carbons to 1 long
chain branches/1000 carbons.
Long chain branching is defined herein as a branch having a chain
length greater than that of any short chain branches which are a
result of comonomer incorporation. The long chain branch can be as
long as about the same length as the length of the polymer
back-bone.
Long chain branching can be determined by using .sup.13 C nuclear
magnetic resonance (NMR) spectroscopy and is quantified using the
method of Randall (Rev. Macromol. Chem. Phys., C29 (2&3), p.
275-287), the disclosure of which is incorporated herein by
reference.
In the case of substantially linear ethylene polymers, such
polymers can be characterized as having:
a) a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63,
b) a molecular weight distribution, M.sub.w /M.sub.n, defined by
the equation:
and
c) a critical shear stress at onset of gross melt fracture greater
than 4.times.10.sup.6 dynes/cm.sup.2 or a critical shear rate at
onset of surface melt fracture at least 50 percent greater than the
critical shear rate at the onset of surface melt fracture of either
a homogeneously or heterogeneously branched linear ethylene polymer
having about the same I.sub.2 and M.sub.w /M.sub.n, or both.
In contrast to substantially linear ethylene polymers, linear
ethylene polymers lack long chain branching, i.e., they have less
than 0.01 long chain branches/1000 carbons. The term "linear
ethylene polymers" thus does not refer to high pressure branched
polyethylene, ethylene/vinyl acetate copolymers, or ethylene/vinyl
alcohol copolymers which are known to those skilled in the art to
have numerous long chain branches.
Linear ethylene polymers include, for example, the traditional
heterogeneously branched linear low density polyethylene polymers
or linear high density polyethylene polymers made using Ziegler
polymerization processes (e.g., U.S. Pat. No. 4,076,698 (Anderson
et al.)) the disclosure of which is incorporated herein by
reference), or homogeneous linear polymers (e.g., U.S. Pat. No.
3,645,992 (Elston) the disclosure of which is incorporated herein
by reference).
Both the homogeneous linear and the substantially linear ethylene
polymers used to form the fibers have homogeneous branching
distributions. The term "homogeneously branching distribution"
means that the comonomer is randomly distributed within a given
molecule and that substantially all of the copolymer molecules have
the same ethylene/comonomer ratio. The homogeneous
ethylene/.alpha.-olefin polymers used in this invention essentially
lack a measurable "high density" fraction as measured by the TREF
technique (i.e., the homogeneous branched ethylene/.alpha.-olefin
polymers are characterized as typically having less than 15 weight
percent, preferably less than 10 weight percent, and more
preferably less than 5 weight percent of a polymer fraction with a
degree of branching less than or equal to 2 methyls/1000
carbons).
The homogeneity of the branching distribution can be measured
variously, including measuring the SCBDI (Short Chain Branch
Distribution Index) or CDBI (Composition Distribution Branch
Index). SCBDI or CDBI is defined as the weight percent of the
polymer molecules having a comonomer content within 50 percent of
the median total molar comonomer content. The CDBI of a polymer is
readily calculated from data obtained from techniques known in the
art, such as, for example, temperature rising elusion fractionation
(abbreviated herein as "TREF) as described, for example, in Wild et
al, Journal of Polymer Science, Poly. Phys. Ed., Vol. 20, p. 441
(1982), U.S. Pat. No. 5,008,204 (Stehling), the disclosure of which
is incorporated herein by reference. The technique for calculating
CDBI is described in U.S. Pat. No. 5,322,728 (Davey et al.) and in
U.S. Pat. No. 5,246,783 (Spenadel et al.), both disclosures of
which are incorporated herein by reference. The SCBDI or CDBI for
homogeneously branched linear and substantially linear ethylene
polymers is typically greater than 30 percent, and is preferably
greater than 50 percent, more preferably greater than 60 percent,
even more preferably greater than 70 percent, and most preferably
greater than 90 percent.
The homogeneous branched ethylene polymers used to make the fibers
of the present invention will preferably have a single melting
peak, as measured using differential scanning calorimetry (DSC), in
contrast to heterogeneously branched linear ethylene polymers,
which have 2 or more melting peaks, due to the heterogeneously
branched polymer's broad branching distribution.
Substantially linear ethylene polymers exhibit a highly unexpected
flow property where the I.sub.10 /I.sub.2 value of the polymer is
essentially independent of polydispersity index (i.e., M.sub.w
/M.sub.n) of the polymer. This is contrasted with conventional
homogeneous linear ethylene polymers and heterogeneously branched
linear polyethylene resins for which one must increase the
polydispersity index in order to increase the I.sub.10 /I.sub.2
value. Substantially linear ethylene polymers also exhibit good
processability and low pressure drop through a spinneret pack, even
when using high shear filtration.
Homogeneous linear ethylene polymers useful to make the fibers and
fabrics of the invention are a known class of polymers which have a
linear polymer backbone, no long chain branching and a narrow
molecular weight distribution. Such polymers are interpolymers of
ethylene and at least one .alpha.-olefin comonomer of from 3 to 20
carbon atoms, and are preferably copolymers of ethylene with a
C.sub.3 -C.sub.20 .alpha.-olefin, and are most preferably
copolymers of ethylene with propylene, 1-butene, 1-hexene,
4-methyl-1-pentene or 1-octene. This class of polymers is disclosed
for example, by Elston in U.S. Pat. No. 3,645,992 and subsequent
processes to produce such polymers using metallocene catalysts have
been developed, as shown, for example, in EP 0 129 368, EP 0 260
999, U.S. Pat. Nos. 4,701,432; 4,937,301; 4,935,397; 5,055,438; and
WO 90/07526, and others. The polymers can be made by conventional
polymerization processes (e.g., gas phase, slurry, solution, and
high pressure).
Another measurement useful in characterizing the molecular weight
of ethylene polymers is conveniently indicated using a melt index
measurement according to ASTM D-1238, Condition 190.degree. C./10
kg (formerly known as "Condition (N)" and also known as I.sub.10).
The ratio of these two melt index terms is the melt flow ratio and
is designated as I.sub.10 /I.sub.2. For the substantially linear
ethylene polymers used polymer compositions useful in making the
fibers of the invention, the I.sub.10 /I.sub.2 ratio indicates the
degree of long chain branching, i.e., the higher the I.sub.10
/I.sub.2 ratio, the more long chain branching in the polymer. The
substantially linear ethylene polymers can have varying I.sub.10
/I.sub.2 ratios, while maintaining a low molecular weight
distribution (i.e., M.sub.w /M.sub.n from 1.5 to 2.5). Generally,
the I.sub.10 /I.sub.2 ratio of the substantially linear ethylene
polymers is at least 5.63, preferably at least 6, more preferably
at least 7, and especially at least 8. Generally, the upper limit
of I.sub.10 /I.sub.2 ratio for the homogeneously branched
substantially linear ethylene polymers is 50 or less, preferably 30
or less, and especially 20 or less.
Additives such as antioxidants (e.g., hindered phenolics (e.g.,
Irganox.TM.1010 made by Ciba-Geigy Corp.), phosphites (e.g.,
Irgafos.TM.) 168 made by Ciba-Geigy Corp.), cling additives (e.g.,
polyisobutylene (PIB)), antiblock additives, pigments, can also be
included in the first polymer, the second polymer, or the overall
polymer composition useful to make the fibers and fabrics of the
invention, to the extent that they do not interfere with the
enhanced fiber and fabric properties discovered by Applicants.
The molecular weight distributions of ethylene polymers are
determined by gel permeation chromatography (GPC) on a Waters 150
C. high temperature chromatographic unit equipped with a
differential refractometer and three columns of mixed porosity. The
columns are supplied by Polymer Laboratories and are commonly
packed with pore sizes of 10.sup.3, 10.sup.4, 10.sup.5 and 10.sup.6
.ANG..; The solvent is 1,2,4-trichlorobenzene, from which about 0.3
percent by weight solutions of the samples are prepared for
injection. The flow rate is about 1.0 milliliters/minute, unit
operating temperature is about 140.degree. C. and the injection
size is about 100 microliters.
The molecular weight determination with respect to the polymer
backbone is deduced by using narrow molecular weight distribution
polystyrene standards (from Polymer Laboratories) in conjunction
with their elution volumes. The equivalent polyethylene molecular
weights are determined by using appropriate Mark-Houwink
coefficients for polyethylene and polystyrene (as described by
Williams and Ward in Journal of Polymer Science Polymer Letters,
Vol. 6, p. 621, 1968) to derive the following equation:
In this equation, a=0.4316 and b=1.0. Weight average molecular
weight, Mw, is calculated in the usual manner according to the
following formula: M.sub.j =(.SIGMA.w.sub.i (M.sub.i.sup.j)).sup.j
; where w.sub.i is the weight fraction of the molecules with
molecular weight M.sub.i eluting from the GPC column in fraction i
and j=1 when calculating.sub.Mw and j=-1 when calculating M.sub.n.
The novel composition has M.sub.w /M.sub.n less than or equal to
3.3, preferably less than or equal to 3, and especially in the
range of from about 2.4 to about 3.
The M.sub.w /M.sub.n of the substantially linear homogeneously
branched ethylene polymers is defined by the equation:
Preferably, the Mw/Mn for the ethylene polymers is from 1.5 to 2.5,
and especially from 1.8 to 2.2.
An apparent shear stress versus apparent shear rate plot is used to
identify the melt fracture phenomena. According to Ramamurthy in
Journal of Rheology, 30(2), 337-357, 1986, above a certain critical
flow rate, the observed extrudate irregularities may be broadly
classified into two main types: surface melt fracture and gross
melt fracture.
Surface melt fracture occurs under apparently steady flow
conditions and ranges in detail from loss of specular gloss to the
more severe form of "sharkskin". In this disclosure, the onset of
surface melt fracture is characterized at the beginning of losing
extrudate gloss at which the surface roughness of extrudate can
only be detected by 40.times. magnification. The critical shear
rate at onset of surface melt fracture for a substantially linear
ethylene polymer is at least 50 percent greater than the critical
shear rate at the onset of surface melt fracture of a homogeneous
linear ethylene polymer having the same I.sub.2 and M.sub.w
/M.sub.n.
Gross melt fracture occurs at unsteady flow conditions and ranges
in detail from regular (alternating rough and smooth, helical,
etc.) to random distortions. For commercial acceptability, (e.g.,
in blown film products), surface defects should be minimal, if not
absent. The critical shear rate at onset of surface melt fracture
(OSMF) and onset of gross melt fracture (OGMF) will be used herein
based on the changes of surface roughness and configurations of the
extrudates extruded by a GER.
The gas extrusion rheometer is described by M. Shida, R. N. Shroff
and L. V. Cando in Polymer Engineering Science, Vol. 17, no. 11, p.
770 (1977), and in Rheometers for Molten Plastics by John Dealy,
published by Van Nostrand Reinhold Co. (1982) on page 97, both
publications of which are incorporated by reference herein in their
entirety. All GER experiments are performed at a temperature of
190.degree. C., at nitrogen pressures between 5250 to 500 psig
using a 0.0296 inch diameter, 20:1 L/D die. An apparent shear
stress vs. apparent shear rate plot is used to identify the melt
fracture phenomena. According to Ramamurthy in Journal of Rheology,
30(2), pp. 337-357, 1986, above a certain critical flow rate, the
observed extrudate irregularities may be broadly classified into
two main types: surface melt fracture and gross melt fracture.
For the polymers described herein, the PI is the apparent viscosity
(in Kpoise) of a material measured by GER at a temperature of
190.degree. C., at nitrogen pressure of 2500 psig using a 0.0296
inch diameter, 20:1 L/D die, or corresponding apparent shear stress
of 2.15.times.10.sup.6 dyne/cm.sup.2.
The processing index is measured at a temperature of 190.degree.
C., at nitrogen pressure of 2500 psig using 0.0296 inch diameter,
20:1 L/D die having an entrance angle of 180.degree..
Exemplary constrained geometry catalysts for use in polymerizing
the homogeneously branched substantially linear ethylene polymers
preferentially used to make the novel fibers and other articles of
the present invention preferably include those constrained geometry
catalysts as disclosed in U.S. application Ser. Nos.: 545,403,
filed Jul. 3, 1990; 758,654, now U.S. Pat. No. 5,132,380; 758,660,
now abandoned, filed Sep. 12, 1991; and 720,041, now abandoned,
filed Jun. 24,1991, and in U.S. Pat. Nos. 5,272,236 and 5,278,272,
the disclosures of all of which are incorporated herein by
reference.
As indicated above, substantially random ethylene/vinyl aromatic
interpolymers are especially preferred ethylene polymers for use in
the present invention. Representative of substantially random
ethylene/vinyl aromatic interpolymers are substantially random
ethylene/styrene interpolymers preferably containing at least 20,
more preferably equal to or greater than 30, and most preferably
equal to or greater than 50 weight percent interpolymerized styrene
monomer.
A substantially random interpolymer comprises in polymerized form
i) one or more .alpha.-olefin monomers and ii) one or more vinyl or
vinylidene aromatic monomers and/or one or more sterically hindered
aliphatic or cycloaliphatic vinyl or vinylidene monomers, and
optionally iii) other polymerizable ethylenically unsaturated
monomer(s).
The term "interpolymer" is used herein to indicate a polymer
wherein at least two different monomers are polymerized to make the
interpolymer.
The term "substantially random" in the substantially random
interpolymer resulting from polymerizing i) one or more
.alpha.-olefin monomers and ii) one or more vinyl or vinylidene
aromatic monomers and/or one or more sterically hindered aliphatic
or cycloaliphatic vinyl or vinylidene monomers, and optionally iii)
other polymerizable ethylenically unsaturated monomer(s) as used
herein generally means that the distribution of the monomers of
said interpolymer can be described by the Bernoulli statistical
model or by a first or second order Markovian statistical model, as
described by J. C. Randall in Polymer Sequence Determination.
Carbon-13 NMR Method, Academic Press New York, 1977, pp. 71-78.
Preferably, the substantially random interpolymer resulting from
polymerizing one or more .alpha.-olefin monomers and one or more
vinyl or vinylidene aromatic monomers, and optionally other
polymerizable ethylenically unsaturated monomer(s), does not
contain more than 15 percent of the total amount of vinyl or
vinylidene aromatic monomer in blocks of vinyl or vinylidene
aromatic monomer of more than 3 units. More preferably, the
interpolymer is not characterized by a high degree of either
isotacticity or syndiotacticity. This means that in the carbon-13
NMR spectrum of the substantially random interpolymer, the peak
areas corresponding to the main chain methylene and methine carbons
representing either meso diad sequences or racemic diad sequences
should not exceed 75 percent of the total peak area of the main
chain methylene and methine carbons.
By the subsequently used term "substantially random interpolymer"
it is meant a substantially random interpolymer produced from the
above-mentioned monomers.
Suitable .alpha.-olefin monomers which are useful for preparing the
substantially random interpolymer include, for example,
.alpha.-olefin monomers containing from 2 to 20, preferably from 2
to 12, more preferably from 2 to 8 carbon atoms. Preferred such
monomers include ethylene, propylene, butene-1, 4-methyl-1-pentene,
hexene-1 and octene-1. Most preferred are ethylene or a combination
of ethylene with C.sub.3 -C.sub.8 .alpha.-olefins. These
.alpha.-olefins do not contain an aromatic moiety.
Suitable vinyl or vinylidene aromatic monomers which can be
employed to prepare the substantially random interpolymer include,
for example, those represented by the following formula I
##STR3##
wherein R.sup.1 is selected from the group of radicals consisting
of hydrogen and alkyl radicals containing from 1 to 4 carbon atoms,
preferably hydrogen or methyl; each R.sup.2 is independently
selected from the group of radicals consisting of hydrogen and
alkyl radicals containing from 1 to 4 carbon atoms, preferably
hydrogen or methyl; Ar is a phenyl group or a phenyl group
substituted with from 1 to 5 substituents; selected from the group
consisting of halo, C.sub.1 -C.sub.4 -alkyl, and C.sub.1 -C.sub.4
-haloalkyl; and n has a value from zero to 4, preferably from zero
to 2, most preferably zero. Particularly suitable such monomers
include styrene and lower alkyl- or halogen-substituted derivatives
thereof. Exemplary monovinyl or monovinylidene aromatic monomers
include styrene, vinyl toluene, .alpha.-methylstyrene, t-butyl
styrene or chlorostyrene, including all isomers of these compounds.
Preferred monomers include styrene, .alpha.-methyl styrene, the
lower alkyl-(C.sub.1 -C.sub.4) or phenyl-ring substituted
derivatives of styrene, such as for example, ortho-, meta-, and
para-methylstyrene, the ring halogenated styrenes, para-vinyl
toluene or mixtures thereof. A more preferred aromatic monovinyl
monomer is styrene.
By the term "sterically hindered aliphatic or cycloaliphatic vinyl
or vinylidene monomers", it is meant addition polymerizable vinyl
or vinylidene monomers corresponding to the formula: ##STR4##
wherein A.sup.1 is a sterically bulky, aliphatic or cycloaliphatic
substituent of up to 20 carbons, R.sup.1 is selected from the group
of radicals consisting of hydrogen and alkyl radicals containing
from 1 to 4 carbon atoms, preferably hydrogen or methyl; each
R.sup.2 is independently selected from the group of radicals
consisting of hydrogen and alkyl radicals containing from 1 to 4
carbon atoms, preferably hydrogen or methyl; or alternatively
R.sup.1 and A.sup.1 together form a ring system.
By the term "sterically bulky" is meant that the monomer bearing
this substituent is normally incapable of addition polymerization
by standard Ziegler-Natta polymerization catalysts at a rate
comparable with ethylene polymerizations.
.alpha.-Olefin monomers containing from 2 to about 20 carbon atoms
and having a linear aliphatic structure such as propylene,
butene-1, hexene-1 and octene-1 are not considered as sterically
hindered aliphatic monomers. Preferred sterically hindered
aliphatic or cycloaliphatic vinyl or vinylidene compounds are
monomers in which one of the carbon atoms bearing ethylenic
unsaturation is tertiary or quaternary substituted. Examples of
such substituents include cyclic aliphatic groups such as
cyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl or aryl
substituted derivatives thereof, tert-butyl or norbornyl. Most
preferred sterically hindered aliphatic or cycloaliphatic vinyl or
vinylidene compounds are the various isomeric vinyl-ring
substituted derivatives of cyclohexene and substituted
cyclohexenes, and 5-ethylidene-2-norbornene. Especially suitable
are 1-, 3-, and 4-vinylcyclohexene.
The substantially random interpolymers usually contain from about
0.5 to about 65, preferably from about 1 to about 55, more
preferably from about 2 to about 50 mole percent of at least one
vinyl or vinylidene aromatic monomer and/or sterically hindered
aliphatic or cycloaliphatic vinyl or vinylidene monomer and from
about 35 to about 99.5, preferably from about 45 to about 99, more
preferably from about 50 to about 98 mole percent of at least one
aliphatic .alpha.-olefin having from about 2 to about 20 carbon
atoms.
Other optional polymerizable ethylenically unsaturated monomer(s)
include strained ring olefins such as norbornene and C.sub.1
-C.sub.10 -alkyl or C.sub.6 -C.sub.10 -aryl substituted norbornene,
with an exemplary substantially random interpolymer being
ethylene/styrene/norbornene.
The most preferred substantially random interpolymers are
interpolymers of ethylene and styrene and interpolymers of
ethylene, styrene and at least one .alpha.-olefin containing from 3
to 8 carbon atoms.
The number average molecular weight (M.sub.n) of the substantially
random interpolymers is usually greater than 5,000, preferably from
about 20,000 to about 1,000,000, more preferably from about 50,000
to about 500,000. The glass transition temperature (T.sub.g) of the
substantially random interpolymers is preferably from about
-40.degree. C. to about +35.degree. C., preferably from about
0.degree. C. to about +30.degree. C., most preferably from about
+10.degree. C. to about +25.degree. C., measured according to
differential mechanical scanning (DMS).
The substantially random interpolymers may be modified by typical
grafting, hydrogenation, functionalizing, or other reactions well
known to those skilled in the art. The polymers may be readily
sulfonated or chlorinated to provide functionalized derivatives
according to established techniques. The substantially random
interpolymers may also be modified by various chain extending or
crosslinking processes including, but not limited to peroxide-,
silane-, sulfur-, radiation-, or azide-based cure systems. A full
description of the various crosslinking technologies is described
in copending U.S. patent application Ser. Nos. 08/921,641 and
08/921,642, both filed on Aug. 27, 1997, the entire contents of
both of which are herein incorporated by reference.
Dual cure systems, which use a combination of heat, moisture cure,
and radiation steps, may also be effectively employed. Dual cure
systems are disclosed and claimed in U.S. patent application Ser.
No. 536,022, filed on Sep. 29, 1995, in the names of K. L. Walton
and S. V. Karande, incorporated herein by reference. For instance,
it may be desirable to employ peroxide crosslinking agents in
conjunction with silane crosslinking agents, peroxide crosslinking
agents in conjunction with radiation, sulfur-containing
crosslinking agents in conjunction with silane crosslinking agents,
etc.
The substantially random interpolymers may also be modified by
various crosslinking processes including, but not limited to the
incorporation of a diene component as a termonomer in its
preparation and subsequent crosslinking by the aforementioned
methods and further methods including vulcanization via the vinyl
group using sulfur for example as the cross linking agent.
One suitable method for manufacturing substantially random
ethylene/vinyl aromatic interpolymers includes polymerizing a
mixture of polymerizable monomers in the presence of one or more
metallocene or constrained geometry catalysts in combination with
various cocatalysts, as described in EP-A-0,416,815 by James C.
Stevens et al. and U.S. Pat. No. 5,703,187 by Francis J. Timmers,
both of which are incorporated herein by reference in their
entirety. Preferred operating conditions for such polymerization
reactions include pressures from atmospheric up to 3000 atmospheres
and temperatures from -300.degree. C. to 200.degree. C.
Polymerizations and unreacted monomer removal at temperatures above
the auto-polymerization temperature of the respective monomers may
result in formation of some amounts of homopolymer polymerization
products resulting from free radical polymerization.
Examples of suitable catalysts and methods for preparing the
substantially random interpolymers are disclosed in U.S.
application Ser. No. 702,475, filed May 20, 1991 (EP-A-514,828); as
well as U.S. Pat. Nos.: 5,055,438; 5,057,475; 5,096,867; 5,064,802;
5,132,380; 5,189,192; 5,321,106; 5,347,024; 5,350,723; 5,374,696;
5,399,635; 5,470,993; 5,703,187; and 5,721,185, all of which
patents and applications are incorporated herein by reference.
The substantially random ethylene/vinyl aromatic interpolymers can
also be prepared by the methods described in JP 07/278230 (the
disclosure of which is incorporated herein by reference) employing
compounds shown by the general formula ##STR5##
Where Cp.sup.1 and Cp.sup.2 are cyclopentadienyl groups, indenyl
groups, fluorenyl groups, or substituents of these, independently
of each other; R.sup.1 and R.sup.2 are hydrogen atoms, halogen
atoms, hydrocarbon groups with carbon numbers of 1-12, alkoxyl
groups, or aryloxyl groups, independently of each other; M is a
group IV metal, preferably Zr or Hf, most preferably Zr; and
R.sup.3 is an alkylene group or silanediyl group used to crosslink
Cp.sup.1 and Cp.sup.2.
The substantially random ethylene/vinyl aromatic interpolymers can
also be prepared by the methods described by John G. Bradfute et
al. (W. R. Grace & Co.) in WO 95/32095; by R. B. Pannell (Exxon
Chemical Patents, inc.) in WO 94/00500; and in Plastics Technology
p. 25 (September 1992), all of which are incorporated herein by
reference in their entirety.
Also suitable are the substantially random interpolymers which
comprise at least one .alpha.-olefin/vinyl aromatic/vinyl
aromatic/.alpha.-olefin tetrad disclosed in U.S. application Ser.
No. 08/708,869, filed Sep. 4,1996, and WO 98/09999, both by Francis
J. Timmers et al. These interpolymers contain additional signals in
their carbon-13 NMR spectra with intensities greater than three
times the peak to peak noise. These signals appear in the chemical
shift range 43.70-44.25 ppm and 38.0-38.5 ppm. Specifically, major
peaks are observed at 44.1, 43.9, and 38.2 ppm. A proton test NMR
experiment indicates that the signals in the chemical shift region
43.70-44.25 ppm are methine carbons and the signals in the region
38.0-38.5 ppm are methylene carbons.
It is believed that these new signals are due to sequences
involving two head-to-tail vinyl aromatic monomer insertions
preceded and followed by at least one .alpha.-olefin insertion,
e.g. an ethylene/styrene/styrene/ethylene tetrad wherein the
styrene monomer insertions of said tetrads occur exclusively in a
1,2 (head to tail) manner. It is understood by one skilled in the
art that for such tetrads involving a vinyl aromatic monomer other
than styrene and an .alpha.-olefin other than ethylene that the
ethylene/vinyl aromatic monomer/vinyl aromatic monomer/ethylene
tetrad will give rise to similar carbon-13 NMR peaks but with
slightly different chemical shifts.
These interpolymers can be prepared by conducting the
polymerization at temperatures of from about -30.degree. C. to
about 250.degree. C. in the presence of such catalysts as those
represented by the formula: ##STR6##
wherein each Cp is independently, each occurrence, a substituted
cyclopentadienyl group .pi.-bound to M; E is C or Si; M is a group
IV metal, preferably Zr or Hf, most preferably Zr; each R is
independently, each occurrence, H, hydrocarbyl, silahydrocarbyl, or
hydrocarbylsilyl, containing up to 30, preferably from about 1 to
about 20, more preferably from about 1 to about 10 carbon or
silicon atoms; each R' is independently, each occurrence, H, halo,
hydrocarbyl, hydrocarbyloxy, silahydrocarbyl, hydrocarbylsilyl
containing up to 30, preferably from about 1 to about 20, more
preferably from about 1 to about 10 carbon or silicon atoms or two
R' groups together can be a C.sub.1 -C.sub.10 hydrocarbyl
substituted 1,3-butadiene; M is 1 or 2; and optionally, but
preferably in the presence of an activating cocatalyst.
Particularly, suitable substituted cyclopentadienyl groups include
those illustrated by the formula: ##STR7##
wherein each R is independently, each occurrence, H, hydrocarbyl,
silahydrocarbyl, or hydrocarbylsilyl, containing up to 30,
preferably from about 1 to about 20, more preferably from about 1
to about 10 carbon or silicon atoms or two R groups together form a
divalent derivative of such group. Preferably, R independently each
occurrence is (including where appropriate all isomers) hydrogen,
methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenyl or
silyl or (where appropriate) two such R groups are linked together
forming a fused ring system such as indenyl, fluorenyl,
tetrahydroindenyl, tetrahydrofluorenyl, or octahydrofluorenyl.
Particularly preferred catalysts include, for example,
racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium
dichloride,
racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium
1,4diphenyl-1,3-butadiene,
racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium
di-C.sub.1 -C.sub.4 alkyl,
racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium
di-C.sub.1 -C.sub.4 alkoxide, or any combination thereof and the
like.
It is also possible to use the following titanium-based constrained
geometry catalysts,
[n-(1,1-dimethylethyl)-1,1-dimethyl-I-[(1,2,3,4,5-.eta.)-1,5,6,7-tetrahydr
o-s-indacen-I-yl]silanaminato(2-)-n]titanium dimethyl;
(1-indenyl)(tert-butylamido)dimethyl-silane titanium dimethyl;
((3-tert-butyl)(1,2,3,4,5-.eta.)-I-indenyl)(tert-butylamido)dimethylsilane
titanium dimethyl; and
((3-iso-propyl)(1,2,3,4,5-.eta.)-I-indenyl)(tert-butyl
amido)dimethylsilane titanium dimethyl, or any combination thereof
and the like.
Further preparative methods for the interpolymers used in the
present invention have been described in the literature. Longo and
Grassi (Makromol. Chem. Volume 191, pages 2387 to 2396 [1990]) and
D'Anniello et al. (Journal of Applied Polymer Science, Volume 58,
pages 1701-1706 [1995]) reported the use of a catalytic system
based on methylalumoxane (MAO) and cyclopentadienyl-titanium
trichloride (CpTiC1.sub.3) to prepare an ethylene-styrene
copolymer. Xu and Lin (Polymer Preprints Am. Chem. Soc., Div.
Polym. Chem.), Volume 35, pages 686,687 [1994]) have reported
copolymerization using a MgCl.sub.2 /TiCl.sub.4 /NdCl.sub.3
/Al(iBu).sub.3 catalyst to give random copolymers of styrene and
propylene. Lu et al (Journal of Applied Polymer Science, Volume 53,
pages 1453 to 1460 [1994]) have described the copolymerization of
ethylene and styrene using a TiC1.sub.4 /NdCl.sub.3 /MgCl.sub.2
/al(Et).sub.3 catalyst. Sernetz and Mulhaupt, (Macromol. Chem.
Phys., V. 197, pp. 1071-1083, 1997) have described the influence of
polymerization conditions on the copolymerization of styrene with
ethylene using Me.sub.2 Si(Me.sub.4 Cp)(n-tert-butyl)TiCl.sub.2
/Methylaluminoxane Ziegler-Natta catalysts. Copolymers of ethylene
and styrene produced by bridged metallocene catalysts have been
described by Arai, Toshiaki and Suzuki (Polymer Preprints Am. Chem.
Soc., Div. Polym. Chem.), Volume 38, pages 349, 350 [1997]) and in
U.S. Pat. No. 5,652,315, issued to Mitsui Toatsu Chemicals, Inc.
The manufacture of .alpha.-olefin/vinyl aromatic monomer
interpolymers such as propylene/styrene and butene/styrene are
described in U.S. Pat. No. 5,244,996, issued to Mitsui
Petrochemical Industries Ltd. or U.S. Pat. No. 5,652,315 also
issued to Mitsui Petrochemical Industries Ltd. or as disclosed in
DE 197 11339 A1 to Denki Kagaku Kogyo KK. All of the above
disclosures of methods for preparing the interpolymer component are
incorporated herein by reference. Also, although of high
isotacticity and therefore not "substantially random", the random
copolymers of ethylene and styrene as disclosed in Polymer
Preprints, Vol. 39, no. 1, March 1998 by Toru Aria et al. (the
disclosure of which is incorporated herein by reference) can also
be employed as the ethylene polymer of the present invention.
While preparing the substantially random interpolymer, an amount of
atactic vinyl aromatic homopolymer may be formed due to
homopolymerization of the vinyl aromatic monomer at elevated
temperatures. The presence of vinyl aromatic homopolymer is in
general not detrimental for the purposes of the present invention
and can be tolerated. The vinyl aromatic homopolymer may be
separated from the interpolymer, if desired, by extraction
techniques such as selective precipitation from solution with a
non-solvent for either the interpolymer or the vinyl aromatic
homopolymer. Nevertheless, for the purpose of the present
invention, it is preferred that no more than 30 weight percent,
preferably less than 20 weight percent (based on the total weight
of the interpolymers) of atactic vinyl aromatic homopolymer be is
present.
The polypropylene and ethylene polymers may be produced via a
continuous (as opposed to a batch) controlled polymerization
process using at least one reactor for each polymer. But the
inventive polymer blend composition itself (or a blend comprising
or constituting the polypropylene polymer and/or a separate blend
comprising or constituting the ethylene polymer) can also be
produced using multiple reactors (e.g., using a multiple reactor
configuration as described in U.S. Pat. No. 3,914,342 (Mitchell),
incorporated herein by reference), with the polypropylene polymer
being manufactured in one reactor and the ethylene polymer being
manufactured in at least one other reactor. The multiple reactors
can be operated in series or in parallel, with at least one
constrained geometry catalyst employed in at least one of the
reactors at a polymerization temperature and pressure sufficient to
produce the polypropylene polymer and/or the ethylene polymer
having the desired properties.
According to a preferred embodiment of the present process, the
polymers are produced in a continuous process, as opposed to a
batch process. Preferably, the ethylene polymerization or
interpolymerization temperature is from 20.degree. C. to
250.degree. C., using constrained geometry catalyst technology. If
a narrow molecular weight distribution polymer (M.sub.w M.sub.n of
from 1.5 to 2.5) having a higher I.sub.10 /I.sub.2 ratio (e.g.
I.sub.10 /I.sub.2 of 7 or more, preferably at least 8, especially
at least 9) is desired, the ethylene concentration in the reactor
is preferably not more than 8 percent by weight of the reactor
contents, especially not more than 4 percent by weight of the
reactor contents. Preferably, the polymerization is performed in a
solution polymerization process. Generally, manipulation of
I.sub.10 /I.sub.2 while holding M.sub.w /M.sub.n relatively low for
producing the substantially linear polymers described herein is a
function of reactor temperature and/or ethylene concentration.
Reduced ethylene concentration and higher temperature generally
produces higher I.sub.10 /I.sub.2.
The polymerization conditions for manufacturing the homogeneous
linear or substantially linear ethylene polymers used to make the
fibers of the present invention are generally those useful in the
solution polymerization process, although the application of the
present invention is not limited thereto. Slurry and gas phase
polymerization processes are also believed to be useful, provided
the proper catalysts and polymerization conditions are
employed.
One technique for polymerizing the homogeneous linear ethylene
polymers useful herein is disclosed in U.S. Pat. No. 3,645,992
(Elston), the disclosure of which is incorporated herein by
reference.
In general, the continuous polymerization useful for making the
ethylene polymers used in the present invention may be accomplished
at conditions well known in the prior art for Ziegler-Natta or
Kaminsky-Sinn type polymerization reactions, that is, temperatures
from 0 to 250.degree. C. and pressures from atmospheric to 1000
atmospheres (100 MPa).
The compositions disclosed herein can be formed by any convenient
method, including dry blending the individual components and
subsequently melt mixing or by pre-melt mixing in a separate
extruder (e.g., a Banbury mixer, a Haake mixer, a Brabender
internal mixer, or a twin (or single) screw extruder, including
pelletization extrusion). Preferably, the inventive composition is
formed by melt mixing in a twin-screw co-rotating extruder.
Another suitable technique for making the composition is in-situ
polymerization such as provided in pending U.S. Ser. No.
08/010,958, entitled "Ethylene Interpolymerizations", which was
filed Jan. 29, 1993 in the names of Brian W. S. Kolthammer and
Robert S. Cardwell, the disclosure of which is incorporated herein
in its entirety by reference. U.S. Ser. No. 08/010,958 describes,
inter alia, interpolymerizations of ethylene and C.sub.3 -C.sub.20
alpha-olefins using a homogeneous catalyst in at least one reactor
and a heterogeneous catalyst in at least one other reactor and this
method can be adapted to employ a polypropylene polymerization
reactor as a substitute for the heterogeneous catalyzed ethylene
polymerization reactor or as an additional reactor. That is, the in
situ polymerization can comprise at least three reactors where at
least two reactors provide the ethylene polymer (as a polymer blend
composition) and at least one reactor provide the reactor grade
polypropylene polymer. For in situ polymerizations, the multiple
reactors can be operated sequentially or in parallel. But
preferably, when in situ polymerization is used it is only employed
to provide suitable ethylene polymers (or ethylene polymer blend
compositions) and not the inventive composition itself.
Preferably, the fiber of the invention will be a multiconstituent
or multicomponent fiber. The inventive multiconstituent fiber can
be staple fibers, spunbond fibers, melt blown fibers (using, e.g.,
systems as disclosed in U.S. Pat. Nos. 4,340,563 (Appel et al.),
4,663,220 (Wisneski et al.), 4,668,566 (Braun), 4,322,027 (Reba),
3,860,369, all of which are incorporated herein by reference), gel
spun fibers (e.g., the system disclosed in U.S. Pat. No. 4,413,110
(Kavesh et al.), incorporated herein by reference), and flash spun
fibers (e.g., the system disclosed in U.S. Pat. No. 3,860,369, the
disclosure of which is incorporated herein by reference).
As defined in The Dictionary of Fiber & Textile Technology, by
Hoechst Celanese Corporation, gel spinning refers to "[a] spinning
process in which the primary mechanism of solidification is the
gelling of the polymer solution by cooling to form a gel filament
consisting of precipitated polymer and solvent. Solvent removal is
accomplished following solidification by washing in a liquid bath.
The resultant fibers can be drawn to give a product with high
tensile strength and modulus."
As defined in The Nonwoven Fabrics Handbook, by John R. Starr,
Inc., produced by INDA, Association of the Nonwoven Fabrics
Industry, flash spinning refers to "a modified spunbonding method
in which a polymer solution is extruded and rapid solvent
evaporation occurs so that the individual filaments are disrupted
into a highly fibrillar form and are collected on a screen to form
a web."
Staple fibers can be melt spun (i.e., they can be extruded into the
final fiber diameter directly without additional drawing), or they
can be melt spun into a higher diameter and subsequently hot or
cold drawn to the desired diameter using conventional fiber drawing
techniques. The novel fibers disclosed herein can also be used as
bonding fibers, especially where the novel fibers have a lower
melting point than the surrounding matrix fibers. In a bonding
fiber application, the bonding fiber is typically blended with
other matrix fibers and the entire structure is subjected to heat,
where the bonding fiber melts and bonds the surrounding matrix
fiber. Typical matrix fibers which benefit from use of the novel
fibers includes, but is not limited to: poly(ethylene
terephthalate) fibers; cotton fibers; nylon fibers; other
polypropylene fibers; other heterogeneously branched polyethylene
fibers; and linear polyethylene homopolymer fibers. The diameter of
the matrix fiber can vary depending upon the end use
application.
The inventive multiconstituent fibers can also be used to provide a
sheath/core bicomponent fiber (i.e., one in which the sheath
concentrically surrounds the core). The inventive polymer blend can
be in either the sheath or the core. Different inventive polymer
blends can also be used independently as the sheath and the core in
the same fiber and especially where the sheath component has a
lower melting point than the core component. Other types of
bicomponent fibers are within the scope of the invention as well,
and include such structures as side-by-side fibers (e.g., fibers
having separate regions of polymers, wherein the inventive polymer
blend comprises at least a portion of the fiber's surface). One
embodiment is in a bicomponent fiber wherein the polymer blend
composition disclosed herein is provided in the sheath, and a
higher melting polymer, such as polyester terephthalate or a
different polypropylene is provided in the core.
The shape of the fiber is not limited. For example, typical fiber
have a circular cross sectional shape, but sometimes fibers have
different shapes, such as a trilobal shape, or a flat (i.e.,
"ribbon" like) shape. The fiber disclosed herein is not limited by
the shape of the fiber.
Fiber diameter can be measured and reported in a variety of
fashions. Generally, fiber diameter is measured in denier per
filament. Denier is a textile term which is defined as the grams of
the fiber per 9000 meters of that fiber's length. Monofilament
generally refers to an extruded strand having a denier per filament
greater than 15, usually greater than 30. Fine denier fiber
generally refers to fiber having a denier of 15 or less.
Microdenier (also referred to as "microfiber") generally refers to
fiber having a diameter not greater than 100 micrometers. For the
novel fibers disclosed herein, the diameter can be widely varied.
But the fiber denier can be adjusted to suit the capabilities of
the finished article and as such, would preferably be from 0.5 to
30 denier/filament for melt blown; from 1 to 30 denier/filament for
spunbond; and from 1 to 20,000 denier/filament for continuous wound
filament.
Fabrics made from the inventive fibers include both woven and
nonwoven fabrics. Nonwoven fabrics can be made variously, including
spunlaced (or hydrodynamically entangled) fabrics as disclosed in
U.S. Pat. Nos. 3,485,706 (Evans) and 4,939,016 (Radwanski et al.),
the disclosures of which are incorporated herein by reference; by
carding and thermally bonding staple fibers; by spunbonding
continuous fibers in one continuous operation; or by melt blowing
fibers into fabric and subsequently calendering or thermally
bonding the resultant web. These various nonwoven fabric
manufacturing techniques are well known to those skilled in the art
and the disclosure is not limited to any particular method. Other
structures made from such fibers are also included within the scope
of the invention, including e.g., blends of these novel fibers with
other fibers (e.g., poly(ethylene terephthalate) (PET) or
cotton).
Optional additive materials for use in the present invention
include pigments, antioxidants, stabilizers, surfactants (e.g., as
disclosed in U.S. Pat. Nos. 4,486,552 (Niemann), 4,578,414 (Sawyer
et al.) or 4,835,194 (Bright et al.), the disclosures of all of
which are incorporated herein by reference).
In preferred embodiments of the invention, at bonding temperatures
lower than the peak elongation temperature (where peak elongation
temperature is the temperature of the maximum elongation), fabrics
prepared from fibers of the invention will exhibit a fabric
elongation which is at least 20 percent, more preferably at least
50 percent, and most preferably at least 100 percent greater than
that of fabric prepared with fibers prepared from the unmodified
polypropylene used as the second polymer.
In preferred embodiments of the invention, at bonding temperatures
at least 10.degree. C. less than the peak strength bonding
temperature (i.e., the bonding temperature of the maximum strength
(tenacity)), fabrics prepared from fibers of the invention will
exhibit a fabric strength which is at least 25 percent, more
preferably at least 50 percent, and most preferably at least 70
percent higher than the a fabric prepared from fiber prepared from
the unmodified polypropylene polymer used as the second polymer.
The improvement is particularly important because attaining a given
tenacity at a comparatively lower thermal bonding invariably
promotes the highly desirably performance property of enhanced
fabric softness.
In preferred embodiments of the invention, fibers of the invention
will exhibit a spinnability (maximum draw rpms) which is no more
than 25 percent less than, more preferably no more than 15 percent
less than the spinnability (maximum draw rpms) of fiber prepared
from the unmodified polypropylene polymer used as the second
polymer. Draw rpms may also be correlated to draw pressure on a
spunbond process.
Useful articles which can be made from the polymer compositions
disclosed herein include films, fibers, thermoformed articles,
molded articles (for example, blow molded articles, injection
molded articles and rotomolded articles) and coated articles (for
example, extrusion coatings). Other useful articles included woven
and nonwoven items such as those described in issued U.S. Pat. No.
5,472,775 (Obijeski et al.), incorporated herein by reference.
The subject invention is particularly usefully employed in the
preparation of calendar roll bonded fabrics such as carded staple
fabric or spunbonded fabrics. Exemplary enduse articles include,
but not limited to, diaper and other personal hygiene article
components, disposable clothing (such as hospital garments),
durable clothing (such as insulated outerwear), disposable wipes,
dishcloths, and filter media.
The subject invention is also usefully employed in the bonding of
carpet or upholstery components, and in the bonding and/or
strengthening of other webs (such as industrial shipping sacks,
strapping and rope, lumber wraps, house/construction wraps, pool
covers, geotextiles, and tarpaulins).
The subject invention may further find utility in adhesive
formulations, optionally in combination with one or more
tackifiers, plasticizers, or waxes.
EXAMPLES
In an evaluation to determine the effect of ethylene polymers on
the fiber spinning, bonding and elongation properties of
polypropylene polymers, a minor amount of various ethylene polymers
were separately admixed with a Ziegler-catalyzed isotactic
polypropylene polymer, INSPIRE.TM. H500-35, supplied by The Dow
Chemical Company. The polypropylene polymer was supplied with a
visbroken melt flow rate of 35 g/10 minutes at 230.degree. C./2.16
kg. The various ethylene polymers used in the evaluation are listed
in Table 1.
In this evaluation, polypropylene/ethylene polymer blends were
prepared by tumble dry-blending followed by melt extrusion and
pelletization. To the dry-blends, 1000 ppm Irgafos 168 was added
via a 5 weight percent master batch concentrate comprising
INSPIRE.TM. H500-35 as the carrier resin. The melt extrusion and
pelletization were performed using a co-rotating twin-screw Werner
Pflieder ZSK-30 (30 mm) extruder at a melt temperature of about
190.degree. C. The extruder was equipped with positive conveyance
elements and no negative conveyance elements. The resultant polymer
blends and the control INSPIRE.TM. H500-35 polypropylene polymer
(comparative example 4) were all meltspun into fiber. Table 2
provides the weight percentage information for the various
examples.
TABLE 1 I.sub.2, Melt Product Index, g/10 Density, Resin
Type/Designation min. g/cm.sup.3 EP1 ENGAGE 8150* 0.5 0.87 EP2
ENGAGE 8100* 1 0.87 EP3 ENGAGE 8200* 5 0.87 EP4 AFFINITY PL 1280* 6
0.90 EP5 ESI 5 <15 wt. %.sup..dagger-dbl. EP6 ENGAGE 8400* 30
0.87 EP7 SLEP 30 0.913 EP8 ASPUN 6811A 27 0.941 .sup..dagger-dbl.
Rather than density, the reported value is percent crystallinity as
determined using differential scanning calorimetry (DSC). Except
for the ENGAGE elastomers, all of the above ethylene polymers are
available from The Dow Chemical Company. ESI denotes a
substantially random ethylene/styrene interpolymer which contains
about 30 weight percent styrene interpolymerized with ethylene.
SLEP denotes a homogeneously branched substantially linear
ethylene/1-octene interpolymer manufactured using a constrained
geometry catalyst system in a continuous polymerization reaction
system. ENGAGE is a trademark of Dupont-Dow Elastomers for ethylene
elastomers. AFFINITY is a trademark of The Dow Chemical Company for
ethylene plastomers. Both AFFINITY and ENGAGE resins are
manufactured in a continuous polymerization reaction system. ASPUN
is a trademark of The Dow Chemical Company for fiber-grade linear
low density polyethylene (LLDPE) resins manufactured using a
Ziegler titanium catalysis system.
TABLE 2 Ethylene Weight Percent Ethylene Example Polymer Polymer
Inv. Ex 1 EP1 5 Inv. Ex 2 EP1 1 Inv. Ex 3 EP1 20 Inv. Ex 5 EP2 2
Inv. Ex 6 EP2 10 Comp. Ex 7 EP3 5 Inv. Ex 8 EP4 5 Inv. Ex 9 EP5 5
Comp. Ex 10 EP6 5 Comp. Ex 11 EP7 5 Comp. Ex 12 EP8 5 Comp. Ex 13
EP3 1 Comp. Ex 14 EP6 1 Comp. Ex 15 EP6 10
Fiber spinning was conducted on an Alex James laboratory scale
spinning apparatus (available from Alex James, Inc.). The various
example compositions were fed separately into a 1 inch.times.24
inches single screw extruder, with melt temperature varying from
195.degree. C. to 220.degree. C. The molten example compositions
were forwarded to a Zenith gear pump at 1.752 cc/rev. and through a
triple screen configuration (20/400/20 mesh). The molten example
compositions then exited through a spinneret containing 108 holes,
each with a diameter of 400 .mu.m, wherein the .sup.L /.sub.D of
the holes was 4/1. The molten example compositions were drawn-down
at 0.37 grams/minute from each hole and air cooled by a quench
chamber.
The drawn-down fibers were moved down 3 meters to a 6 inch diameter
feed godet, then a 6 inch diameter winder godet. The godets were
set to 2000-2200 rotations per minute (rpm), imparted no cold
drawing and delivered fibers having diameters in the range of from
about 3.0 to about 3.5 denier. Fiber samples were collected for 2
minutes on the second godet for each example composition and then
cut from the godet. Each example was then cut into 1 inch to 1.5
inch lengths known as staple fibers and allowed to relax for
minimum 24 hours to promote laboratory consistency.
All of the example compositions spun well, providing fine denier
staple fibers. However, the good spinning performance of the
Inventive Examples (all comprising an ethylene polymer having an
I.sub.2 melt index less than or equal to 5 g/10 minutes) was
surprising because the various ethylene polymers used as the blend
component for the inventive compositions do not spin on the
above-described spinning apparatus when used alone. That is, as
taught by Jezic et al. in U.S. Pat. No. 4,839,228, for successful
fiber-spinning, ethylene polymers having an I.sub.2 melt index
greater than or equal to about 12 g/10 minutes are typically used
and not the kind of high molecular weight ethylene polymers
required in the present invention.
The staple fibers of each example composition were weighed out as
1.25 g specimens, typically 4-8 specimens per sample. The 1.25 g
specimens were fed to a SpinLab Rotor Ring 580 set at maximum speed
for 45 seconds to card the fibers and provide an initial web. After
the first carding, the fibers were removed, re-fed to the SpinLab
Rotor Ring 580 unit, and re-carded for another 45 seconds. After
the second carding, a 3.5 inch fiber web for each example was
removed and placed in a 3.5 inch by 12 inch metal feed tray.
A photomicrograph of the cross-section of carded staple fibers of
Inventive Example 1 was taken (FIG. 1). Prior to taking the
photomicrograph, the carded staple fibers were stained with
RuCl.sub.3 /hypochlorite and mounted with Epofix.TM.. The
photomicrograph itself shows, prior to thermal bonding, the
cross-sectional configuration of the polypropylene polymer
(continuous polymer phase) and the ethylene polymer (the
discontinuous phase) is of the island-sea type with the
polypropylene polymer constituting more than 50 percent of the
surface of the carded staple fiber. That is, the discontinuous
phase did not occupy a substantial portion of the fiber surface
prior to thermal bonding. The same result and characteristic is
shown in FIGS. 2 and 3 for Inventive Examples 3 and 9,
respectively. In addition to indicating the discontinuous phase is
distinct, not highly dispersed (relatively larger particles) and
occupies about as much of the surface of the fiber as the weight
percent amount contained therein (i.e., there is no preferential
migration or substantially higher concentration at the surface),
FIG. 3 also shows that the discontinuous substantially random ESI
phase has at least two components. This multi-component
discontinuous phase is shown as substantially circular particles
with dark stained peripheries which may relate to the amount of
atactic polymer present in the interpolymer. In contrast to FIGS.
1-3, FIG. 4 and FIG. 5 indicate that comparative examples are
characterized by a substantially higher degree of dispersion
(smaller discontinuous phase particles) and miscibility between the
phases (less discontinuous phase distinctiveness). FIGS. 1-5 were
all taken at 15,000.times. magnification.
The carded staple fibers of each example composition were bonded
using a two-roll thermal bonding unit (that is, a Beloit Wheeler
Model 700 Laboratory Calendar). The top roll had a 5 inch diameter
and a 12 inch face and consisted of hardened chromed steel embossed
in a square pattern at 20 percent coverage. The bottom roll was the
same, except not embossed. For thermal bonding, the bond rolls were
set at 1000 psi, which was equivalent to 340 pounds per linear inch
(pli) for this unit. The conversion calculation was as follows:
1000 psi-400 psi for lower roll to overcome spring force=600
psi.times.1.988 square inch cylinder area/3.5 inches web width=340
pli.
The temperatures of the bond rolls were set to maintain about a
3.degree. C. differential, with the top roll always being cooler to
minimize sticking. The bond rolls were also set to range in
temperature from about 118.degree. C. to about 137.degree. C. (top
roll temperature) and 115.degree. C. to 134.degree. C. (bottom roll
temperature). The rolls were rotated at 23.6 feet/minutes. The
fiber webs were then passed between the two rolls and removed from
the side opposite the feed area. The resultant nonwoven embossed
fabrics which had a nominal weight basis of 1 ounce per square yard
were then cut into 1 inch.times.4 inches fabric specimens.
Before performance testing, each fabric specimen was weighed and
the weight entered into a computer program. The 1 inch.times.4
inches specimens were positioned lengthwise on a Sintech 10D
tensiometer equipped with a 200 pound load cell, such that 1 inch
at each end of the specimen was clamped in the top and bottom
grips. The specimens were then pulled, one at a time, at 5
inches/minutes to their breaking point. The computer then used the
dimensions of the specimen and the force exerted to calculate the
percent strain (elongation) experienced by the specimen and the
normalized force at break (tensile break which was taken as the
bond strength for the example) in grams. Four measurements were
taken at each bonding temperature for each example. Table 3
provides the thermal bonding bond strength performance results for
the various carded staple fabric examples. Table 4 provides the
thermal bonding elongation performance results for the various
carded staple fabric examples. FIGS. 6-15 provide various
comparisons between Inventive Examples 1, 2, 3, 5, 6, 8 and 9 and
comparative examples 4, 5, 7, 10, 11, 12, 13, 14 and 15.
TABLE 3 Bond Strength, grams Top Roll, embossed, Temp., .degree. C.
118 120 123 127 130 133 137 Inv. Ex 1 ND ND 2769 3272 3251 4075
4457 Inv. Ex 2 1842 1928 2150 2756 2704 3578 3975 Inv. Ex 3 3509
4039 4337 4551 4289 4133 4329 Comp. Ex 4 1843 2028 1831 2332 2464
3278 3431 Inv. Ex 5 2051 2100 3387 2784 2909 4080 4491 Inv. Ex 6
3240 3367 3558 3936 4110 4897 4574 Comp. Ex 7 1781 1809 2171 2545
2403 2965 3610 Inv. Ex 8 1992 2129 2009 2626 2672 3454 4389 Inv. Ex
9 3029 3307 3344 3886 4468 4497 3646 Comp. Ex 10 1780 1774 1819
2092 2764 3542 3560 Comp. Ex 11 1651 1625 1695 2043 2507 3125 3970
Comp. Ex 12 1692 1738 1961 2161 2488 3301 3772 Comp. Ex 13 2095
2054 2037 2275 2251 3295 4311 Comp. Ex 14 1528 1630 2146 1965 2083
3047 3659 Comp. Ex 15 1914 2198 2111 2493 2882 3167 3745
Table 3 and FIGS. 6-10 show all Inventive Examples, at a top
embossed roll temperature of 127-130.degree. C., are generally
characterized as having bond strengths greater than or equal 2,500
grams and Inventive Examples 1, 3, 6 and 9 are preferentially
characterized as having dramatically improved bond strengths at
greater than or equal to 3,250 gram. That is, bond strengths of
Inventive Examples 1, 3, 6 and 9 were greater than 36 percent
higher (and up to 84 percent) higher than the bond strength of the
polypropylene polymer at a top embossed roll temperature of
127-130.degree. C.
Table 3 and FIGS. 6-10 also show where the I.sub.2 melt index of
the ethylene polymer is relatively high (that is, greater than or
equal to 5 g/10 minutes) and the ethylene polymer is an
ethylene/.quadrature.-olefin interpolymer (for example, where the
.alpha.-olefin is 1-hexene, 1-butene or 1-octene), the inventive
composition will be characterized as comprising an ethylene polymer
which has a polymer density greater than 0.87 g/cm.sup.3,
preferably greater than or equal 0.90 g/cm.sup.3, and more
preferably greater than or equal to 0.94 g/cm.sup.3.
TABLE 4 Percent Elongation Top Roll, embossed, Temp., .degree. C.
118 120 123 127 130 133 137 Inv. Ex 1 ND ND 20 23 27 36 37 Inv. Ex
2 11 12 12 17 18 24 28 Inv. Ex 3 42 56 53 60 55 50 54 Comp. Ex 4 11
11 12 14 14 19 23 Inv. Ex 5 13 12 18 21 20 33 39 Inv. Ex 6 24 27 27
30 35 44 41 Comp. Ex 7 11 12 13 14 17 22 25 Inv. Ex 8 15 15 13 19
19 25 36 Inv. Ex 9 55 66 106 127 107 105 60 Inv. Ex 10 69 73 69 83
90 75 45 Comp. Ex 11 13 14 14 16 20 27 30 Comp. Ex 12 11 11 11 13
16 22 32 Comp. Ex 13 11 11 12 14 16 25 32 Comp. Ex 14 15 14 14 15
18 24 36 Comp. Ex 15 9 10 11 11 12 19 24 Comp. Ex 16 16 16 18 19 21
26 30
Further, Table 3 and FIGS. 6-10 also show that in addition to
ethylene/.alpha.-olefin interpolymers (Inventive Examples 1, 3 and
6), other high molecular weight ethylene polymers such as high
molecular weight ethylene/styrene interpolymers (Inventive Example
9) can dramatically improve the fiber bond strength of isotactic
polypropylene polymers. This data also suggests that the same
result can be obtained with high molecular weight ethylene
homopolymers (HMW-HDPE).
FIGS. 11-15 and Table 4 show that in addition to improved bond
strength, the inventive composition also provides improved fiber
elongation; that is, at a thermal bonding temperature of
127-130.degree. C., all inventive compositions had elongations
greater than 15 percent and preferred inventive compositions
(Inventive Examples 3, 6 and 9) had elongations greater than or
equal to 30 percent at a thermal bonding temperature of
127-130.degree. C. This result is surprising and unexpected because
bond strength improvements tend to reduce elongation performance
(and vice versa). For example, comparative example 10 had a lower
bond strength at 127.degree. C. than the polypropylene polymer
while this comparative example also had a higher percent elongation
than the polypropylene polymer at 127.degree. C.
In another evaluation, the effect of blending a minor amount of a
high molecular weight ethylene polymer in a Ziegler-catalyzed
polypropylene polymer and a metallocene-catalyzed polypropylene
polymer was investigated. The Ziegler-catalyzed polypropylene
polymer and the high molecular weight ethylene polymer (EP2) were
the same as used in Inventive Example 5 above. The reactor grade
metallocene-catalyzed polypropylene polymer in the evaluation had a
MFR of 22 g/10 minutes melt flow rate (ASTM D-1238, Condition
230.degree. C./2.16 kg) and was sold under the designation of
ACHIEVE 3904 by Exxon Chemical Corporation.
This evaluation consisted of four different polymer compositions;
each polypropylene polymer was evaluated as a control resin and for
the other two examples, each polypropylene polymer was melt
blended/extruded with 1000 ppm Irgafos 168 and 5 weight percent of
ENGAGE Elastomer 8100 (an ethylene/1-octene interpolymer supplied
by Dupont-Dow Elastomers) using the above-described master batch
concentrate and ZSK-30 extruder at about 190.degree. C. Each
control propylene polymer was also melt blended/extruded with 1000
ppm Irgafos 168 using the above-described master batch concentrate
and the ZSK-30 extruder at about 190.degree. C. The polypropylene
polymer/ethylene polymer blend that comprised the Ziegler-catalyzed
polypropylene polymer was designated Inventive Example 16. The
polypropylene polymer/ethylene polymer blend that comprised the
metallocene-catalyzed polypropylene polymer was designated
Inventive Example 17. The Ziegler-catalyzed polypropylene polymer
was designated comparative example 18 and the ACHIEVE 3904
metallocene-catalyzed polypropylene polymer was designated
comparative example 19. Each polymer composition was spun into fine
denier staple fibers as described above for Inventive Example 1 and
was also carded as described above. The carded staple fibers for
were tested for bond performance using the same methods and
procedures described above for Inventive Example 1. FIG. 16
graphically shows the thermal bonding performance results for the
four example compositions. The results in FIG. 12 indicate that a
high weight ethylene polymer at nominal amounts can dramatically
improve the thermal bonding performance of both isotactic and
metallocene-polypropylene polymers and that improvements are
especially substantial and surprising stable across a broad bond
temperature range with the metallocene-polypropylene polymer.
FIGS. 17-20 are photomicrograph of thermally bonded fibers. FIG. 17
shows that very little shrink or stress is associated with the
inventive fiber (FIG. 17(b)) relative to the comparative fiber
(FIG. 17(d)). FIG. 18 shows that substantially more melting and
flowing is associated with the inventive fiber (FIGS. 18(a) and
(b)) relative to the comparative fiber (FIGS. 18(c) and (d)). FIG.
19 shows at least four different inventive fibers at different
viewing perspectives at a thermal bonded site magnified
15,000.times.. The different perspectives show, for the inventive
fiber (Inventive Example 1), the discontinuous ethylene polymer
phase (dark stained areas) does not occupy a substantial portion of
a respective fiber surface after thermal bonding. At 15,000.times.
magnification, FIG. 20 shows there is some crazing associated with
polypropylene polymers.
In another evaluation to investigate thermal bonding performance, a
minor amount of various high molecular weight ethylene polymers
were separately blended with a visbroken Ziegler-catalyzed
polypropylene polymer and compared to the neat visbroken
Ziegler-catalyzed polypropylene polymer, a neat reactor grade
metallocene-catalyzed polypropylene polymer and a neat reactor
grade Ziegler-catalyzed polypropylene polymer. The visbroken
Ziegler-catalyzed polypropylene polymer (comparative example 18)
was the same as used in Inventive Example 1 above. The reactor
grade metallocene-catalyzed polypropylene polymer (comparative
example 19) was the same above; that is, it had a MFR of 22 g/10
minutes melt flow rate (ASTM D-1238, Condition 230.degree. C./2.16
kg) and was sold under the designation of ACHIEVE 3904 by Exxon
Chemical Corporation. The reactor grade Ziegler-catalyzed
polypropylene polymer (comparative example 20) had a MFR of 25 g/10
minutes melt flow rate (ASTM D-1238, Condition 230.degree. C./2.16
kg).
The various high molecular weight ethylene polymers used in this
evaluation are listed in Table 5 below.
TABLE 5 I.sub.2, Melt Product Index, g/10 Density, Resin
Type/Designation min. g/cm.sup.3 EP9 HDPE 05862 5 0.962 EP10 SLEP
0.7 0.960 EP11 ESI DE 100 0.5 30 wt. %.sup..dagger-dbl. EP12 ESI DS
100 0.5 70 wt. %.sup..dagger-dbl. EP13 ENGAGE* 8180 0.5 0.863
.sup..dagger-dbl. Rather than density, the reported value is weight
percent styrene. Except for ENGAGE 8180, all of the above ethylene
polymers are available from The Dow Chemical Company. ESI denotes a
substantially random ethylene/styrene interpolymer. SLEP denotes a
homogeneously branched substantially linear ethylene/1-octene
interpolymer manufactured using a constrained geometry catalyst
system in a continuous polymerization reaction system. ENGAGE is a
trademark of Dupont-Dow Elastomers for ethylene elastomers. ENGAGE
elastomers are manufactured in a continuous polymerization reaction
system using a constrained geometry catalyst system. HDPE 05862
manufactured using a Ziegler catalysis system.
Table 6 below provides the polymer weight percentage information
for the examples investigated in this evaluation.
TABLE 6 Ethylene Weight Percent Ethylene Example Polymer Polymer
Comp. Ex 21 EP9 5 Inv. Ex 22 EP10 5 Comp. Ex 23 EP11 5 Inv. Ex 24
EP12 5 Inv. Ex 25 EP10/EP13 2.5/2.5 Comp. Ex 26 EP9 8
Each of the ethylene polymer/polypropylene polymer combinations
were melt blended/extruded with 1000 ppm Irgafos 168 on a ZSK-30
twin-screw co-rotating extruder at about 190.degree. C. Comparative
example 18, a control propylene polymer, was also melt
blended/extruded with 1000 ppm Irgafos 168 the ZSK-30 extruder at
about 190.degree. C.
Each polymer composition was spun into fine denier staple fibers as
described above for Inventive Example 1 and was also carded as
described above. The carded staple fibers for were tested for bond
performance using the same methods and procedures described above
for Inventive Example 1. Table 7 provides the thermal bonding bond
strength (tenacity) performance results at 1 oz/yd.sup.2 for the
various carded staple fabric examples. Table 8 provides the thermal
bonding elongation performance results at 1 oz/yd.sup.2 for the
various carded staple fabric examples.
TABLE 7 Bond Strength, grams Top Roll, embossed, Temp., .degree. C.
120 123 127 130 133 137 140 Comp. Ex 18 1608 1553 1836 1813 2112
3165 3725 Comp. Ex 19 ND 2080 1825 2288 2361 3263 3573 Comp. Ex 20
ND 1816 1776 2024 2043 2559 2839 Comp. Ex 21 1608 1643 2025 2001
2532 3113 3980 Inv. Ex 22 2545 2709 3157 3872 4693 4872 4644 Comp.
Ex 23 1965 2237 2249 2479 2899 3452 4231 Inv. Ex 24 2117 2521 2829
3100 3637 3836 5048 Inv. Ex 25 2288 2792 3383 3851 4092 4780 4329
Comp. Ex 26 ND 1817 2217 2492 2709 3312 4640
TABLE 7 Bond Strength, grams Top Roll, embossed, Temp., .degree. C.
120 123 127 130 133 137 140 Comp. Ex 18 1608 1553 1836 1813 2112
3165 3725 Comp. Ex 19 ND 2080 1825 2288 2361 3263 3573 Comp. Ex 20
ND 1816 1776 2024 2043 2559 2839 Comp. Ex 21 1608 1643 2025 2001
2532 3113 3980 Inv. Ex 22 2545 2709 3157 3872 4693 4872 4644 Comp.
Ex 23 1965 2237 2249 2479 2899 3452 4231 Inv. Ex 24 2117 2521 2829
3100 3637 3836 5048 Inv. Ex 25 2288 2792 3383 3851 4092 4780 4329
Comp. Ex 26 ND 1817 2217 2492 2709 3312 4640
Table 7 shows all Inventive Examples, at a top embossed roll
temperature of 127-130.degree. C., are generally characterized as
having bond strengths greater than or equal 2,500 grams. That is,
in this bond temperature range, the bond strengths of Inventive
Examples 22, 24 and 25 were about 26 to about 114 percent higher
(than the bond strengths of the neat polypropylene polymer
compositions (comparative examples 18, 19 and 20) and the
composition comprising 5 g/10 minutes I.sub.2 Ziegler-catalyzed
HDPE (comparative example 21). Table 7 also shows that for
ethylene/styrene interpolymers comprising 30 weight percent styrene
or less, the I.sub.2 melt index must be in the range of greater
than 0.5 g/10 minutes to less than or equal to 10 g/10 minutes to
ensure substantially improved tenacity.
Table 8 shows the inventive composition provides even more dramatic
improvements in respect of elongation. Specifically, at a top
embossed roll temperature of 127-130.degree. C., the percent
elongations of Inventive Examples 22, 24 and 25 were about 28
percent up to 450 percent higher than the percent elongations of
comparative examples 18, 19, 20 and 21.
* * * * *